Heart Rate: The number of times the HEART VENTRICLES contract per unit of time, usually per minute.Heart: The hollow, muscular organ that maintains the circulation of the blood.Heart Rate, Fetal: The heart rate of the FETUS. The normal range at term is between 120 and 160 beats per minute.Heart Failure: A heterogeneous condition in which the heart is unable to pump out sufficient blood to meet the metabolic need of the body. Heart failure can be caused by structural defects, functional abnormalities (VENTRICULAR DYSFUNCTION), or a sudden overload beyond its capacity. Chronic heart failure is more common than acute heart failure which results from sudden insult to cardiac function, such as MYOCARDIAL INFARCTION.Blood Pressure: PRESSURE of the BLOOD on the ARTERIES and other BLOOD VESSELS.Autonomic Nervous System: The ENTERIC NERVOUS SYSTEM; PARASYMPATHETIC NERVOUS SYSTEM; and SYMPATHETIC NERVOUS SYSTEM taken together. Generally speaking, the autonomic nervous system regulates the internal environment during both peaceful activity and physical or emotional stress. Autonomic activity is controlled and integrated by the CENTRAL NERVOUS SYSTEM, especially the HYPOTHALAMUS and the SOLITARY NUCLEUS, which receive information relayed from VISCERAL AFFERENTS.Heart Diseases: Pathological conditions involving the HEART including its structural and functional abnormalities.Hemodynamics: The movement and the forces involved in the movement of the blood through the CARDIOVASCULAR SYSTEM.Heart Transplantation: The transference of a heart from one human or animal to another.Heart Defects, Congenital: Developmental abnormalities involving structures of the heart. These defects are present at birth but may be discovered later in life.Electrocardiography: Recording of the moment-to-moment electromotive forces of the HEART as projected onto various sites on the body's surface, delineated as a scalar function of time. The recording is monitored by a tracing on slow moving chart paper or by observing it on a cardioscope, which is a CATHODE RAY TUBE DISPLAY.Fetal Heart: The heart of the fetus of any viviparous animal. It refers to the heart in the postembryonic period and is differentiated from the embryonic heart (HEART/embryology) only on the basis of time.Sympathetic Nervous System: The thoracolumbar division of the autonomic nervous system. Sympathetic preganglionic fibers originate in neurons of the intermediolateral column of the spinal cord and project to the paravertebral and prevertebral ganglia, which in turn project to target organs. The sympathetic nervous system mediates the body's response to stressful situations, i.e., the fight or flight reactions. It often acts reciprocally to the parasympathetic system.Electrocardiography, Ambulatory: Method in which prolonged electrocardiographic recordings are made on a portable tape recorder (Holter-type system) or solid-state device ("real-time" system), while the patient undergoes normal daily activities. It is useful in the diagnosis and management of intermittent cardiac arrhythmias and transient myocardial ischemia.Baroreflex: A response by the BARORECEPTORS to increased BLOOD PRESSURE. Increased pressure stretches BLOOD VESSELS which activates the baroreceptors in the vessel walls. The net response of the CENTRAL NERVOUS SYSTEM is a reduction of central sympathetic outflow. This reduces blood pressure both by decreasing peripheral VASCULAR RESISTANCE and by lowering CARDIAC OUTPUT. Because the baroreceptors are tonically active, the baroreflex can compensate rapidly for both increases and decreases in blood pressure.Heart Atria: The chambers of the heart, to which the BLOOD returns from the circulation.Adrenergic beta-Antagonists: Drugs that bind to but do not activate beta-adrenergic receptors thereby blocking the actions of beta-adrenergic agonists. Adrenergic beta-antagonists are used for treatment of hypertension, cardiac arrhythmias, angina pectoris, glaucoma, migraine headaches, and anxiety.Exercise Test: Controlled physical activity which is performed in order to allow assessment of physiological functions, particularly cardiovascular and pulmonary, but also aerobic capacity. Maximal (most intense) exercise is usually required but submaximal exercise is also used.Dogs: The domestic dog, Canis familiaris, comprising about 400 breeds, of the carnivore family CANIDAE. They are worldwide in distribution and live in association with people. (Walker's Mammals of the World, 5th ed, p1065)Heart Block: Impaired conduction of cardiac impulse that can occur anywhere along the conduction pathway, such as between the SINOATRIAL NODE and the right atrium (SA block) or between atria and ventricles (AV block). Heart blocks can be classified by the duration, frequency, or completeness of conduction block. Reversibility depends on the degree of structural or functional defects.Time Factors: Elements of limited time intervals, contributing to particular results or situations.Bradycardia: Cardiac arrhythmias that are characterized by excessively slow HEART RATE, usually below 50 beats per minute in human adults. They can be classified broadly into SINOATRIAL NODE dysfunction and ATRIOVENTRICULAR BLOCK.Myocardium: The muscle tissue of the HEART. It is composed of striated, involuntary muscle cells (MYOCYTES, CARDIAC) connected to form the contractile pump to generate blood flow.Oxygen Consumption: The rate at which oxygen is used by a tissue; microliters of oxygen STPD used per milligram of tissue per hour; the rate at which oxygen enters the blood from alveolar gas, equal in the steady state to the consumption of oxygen by tissue metabolism throughout the body. (Stedman, 25th ed, p346)Heart Valves: Flaps of tissue that prevent regurgitation of BLOOD from the HEART VENTRICLES to the HEART ATRIA or from the PULMONARY ARTERIES or AORTA to the ventricles.Tachycardia: Abnormally rapid heartbeat, usually with a HEART RATE above 100 beats per minute for adults. Tachycardia accompanied by disturbance in the cardiac depolarization (cardiac arrhythmia) is called tachyarrhythmia.Myocardial Contraction: Contractile activity of the MYOCARDIUM.Telemetry: Transmission of the readings of instruments to a remote location by means of wires, radio waves, or other means. (McGraw-Hill Dictionary of Scientific and Technical Terms, 4th ed)Parasympathetic Nervous System: The craniosacral division of the autonomic nervous system. The cell bodies of the parasympathetic preganglionic fibers are in brain stem nuclei and in the sacral spinal cord. They synapse in cranial autonomic ganglia or in terminal ganglia near target organs. The parasympathetic nervous system generally acts to conserve resources and restore homeostasis, often with effects reciprocal to the sympathetic nervous system.Propranolol: A widely used non-cardioselective beta-adrenergic antagonist. Propranolol has been used for MYOCARDIAL INFARCTION; ARRHYTHMIA; ANGINA PECTORIS; HYPERTENSION; HYPERTHYROIDISM; MIGRAINE; PHEOCHROMOCYTOMA; and ANXIETY but adverse effects instigate replacement by newer drugs.Heart Function Tests: Examinations used to diagnose and treat heart conditions.Stroke Volume: The amount of BLOOD pumped out of the HEART per beat, not to be confused with cardiac output (volume/time). It is calculated as the difference between the end-diastolic volume and the end-systolic volume.Ventricular Function, Left: The hemodynamic and electrophysiological action of the left HEART VENTRICLE. Its measurement is an important aspect of the clinical evaluation of patients with heart disease to determine the effects of the disease on cardiac performance.Cardiac Pacing, Artificial: Regulation of the rate of contraction of the heart muscles by an artificial pacemaker.Physical Exertion: Expenditure of energy during PHYSICAL ACTIVITY. Intensity of exertion may be measured by rate of OXYGEN CONSUMPTION; HEAT produced, or HEART RATE. Perceived exertion, a psychological measure of exertion, is included.Cardiovascular Physiological Phenomena: Processes and properties of the CARDIOVASCULAR SYSTEM as a whole or of any of its parts.Respiration: The act of breathing with the LUNGS, consisting of INHALATION, or the taking into the lungs of the ambient air, and of EXHALATION, or the expelling of the modified air which contains more CARBON DIOXIDE than the air taken in (Blakiston's Gould Medical Dictionary, 4th ed.). This does not include tissue respiration (= OXYGEN CONSUMPTION) or cell respiration (= CELL RESPIRATION).Cardiac Output: The volume of BLOOD passing through the HEART per unit of time. It is usually expressed as liters (volume) per minute so as not to be confused with STROKE VOLUME (volume per beat).Myocardial Ischemia: A disorder of cardiac function caused by insufficient blood flow to the muscle tissue of the heart. The decreased blood flow may be due to narrowing of the coronary arteries (CORONARY ARTERY DISEASE), to obstruction by a thrombus (CORONARY THROMBOSIS), or less commonly, to diffuse narrowing of arterioles and other small vessels within the heart. Severe interruption of the blood supply to the myocardial tissue may result in necrosis of cardiac muscle (MYOCARDIAL INFARCTION).Cardiovascular System: The HEART and the BLOOD VESSELS by which BLOOD is pumped and circulated through the body.Sinoatrial Node: The small mass of modified cardiac muscle fibers located at the junction of the superior vena cava (VENA CAVA, SUPERIOR) and right atrium. Contraction impulses probably start in this node, spread over the atrium (HEART ATRIUM) and are then transmitted by the atrioventricular bundle (BUNDLE OF HIS) to the ventricle (HEART VENTRICLE).Atropine: An alkaloid, originally from Atropa belladonna, but found in other plants, mainly SOLANACEAE. Hyoscyamine is the 3(S)-endo isomer of atropine.Exercise: Physical activity which is usually regular and done with the intention of improving or maintaining PHYSICAL FITNESS or HEALTH. Contrast with PHYSICAL EXERTION which is concerned largely with the physiologic and metabolic response to energy expenditure.Arrhythmias, Cardiac: Any disturbances of the normal rhythmic beating of the heart or MYOCARDIAL CONTRACTION. Cardiac arrhythmias can be classified by the abnormalities in HEART RATE, disorders of electrical impulse generation, or impulse conduction.Propanolamines: AMINO ALCOHOLS containing the propanolamine (NH2CH2CHOHCH2) group and its derivatives.Pressoreceptors: Receptors in the vascular system, particularly the aorta and carotid sinus, which are sensitive to stretch of the vessel walls.Coronary Disease: An imbalance between myocardial functional requirements and the capacity of the CORONARY VESSELS to supply sufficient blood flow. It is a form of MYOCARDIAL ISCHEMIA (insufficient blood supply to the heart muscle) caused by a decreased capacity of the coronary vessels.Arrhythmia, Sinus: Irregular HEART RATE caused by abnormal function of the SINOATRIAL NODE. It is characterized by a greater than 10% change between the maximum and the minimum sinus cycle length or 120 milliseconds.Cardiotonic Agents: Agents that have a strengthening effect on the heart or that can increase cardiac output. They may be CARDIAC GLYCOSIDES; SYMPATHOMIMETICS; or other drugs. They are used after MYOCARDIAL INFARCT; CARDIAC SURGICAL PROCEDURES; in SHOCK; or in congestive heart failure (HEART FAILURE).Ventricular Premature Complexes: A type of cardiac arrhythmia with premature contractions of the HEART VENTRICLES. It is characterized by the premature QRS complex on ECG that is of abnormal shape and great duration (generally >129 msec). It is the most common form of all cardiac arrhythmias. Premature ventricular complexes have no clinical significance except in concurrence with heart diseases.Norepinephrine: Precursor of epinephrine that is secreted by the adrenal medulla and is a widespread central and autonomic neurotransmitter. Norepinephrine is the principal transmitter of most postganglionic sympathetic fibers and of the diffuse projection system in the brain arising from the locus ceruleus. It is also found in plants and is used pharmacologically as a sympathomimetic.Models, Cardiovascular: Theoretical representations that simulate the behavior or activity of the cardiovascular system, processes, or phenomena; includes the use of mathematical equations, computers and other electronic equipment.Heart Arrest, Induced: A procedure to stop the contraction of MYOCARDIUM during HEART SURGERY. It is usually achieved with the use of chemicals (CARDIOPLEGIC SOLUTIONS) or cold temperature (such as chilled perfusate).Echocardiography: Ultrasonic recording of the size, motion, and composition of the heart and surrounding tissues. The standard approach is transthoracic.Reflex: An involuntary movement or exercise of function in a part, excited in response to a stimulus applied to the periphery and transmitted to the brain or spinal cord.Rest: Freedom from activity.Isoproterenol: Isopropyl analog of EPINEPHRINE; beta-sympathomimetic that acts on the heart, bronchi, skeletal muscle, alimentary tract, etc. It is used mainly as bronchodilator and heart stimulant.Metoprolol: A selective adrenergic beta-1 blocking agent that is commonly used to treat ANGINA PECTORIS; HYPERTENSION; and CARDIAC ARRHYTHMIAS.Posture: The position or attitude of the body.Myocardial Infarction: NECROSIS of the MYOCARDIUM caused by an obstruction of the blood supply to the heart (CORONARY CIRCULATION).Autonomic Nervous System Diseases: Diseases of the parasympathetic or sympathetic divisions of the AUTONOMIC NERVOUS SYSTEM; which has components located in the CENTRAL NERVOUS SYSTEM and PERIPHERAL NERVOUS SYSTEM. Autonomic dysfunction may be associated with HYPOTHALAMIC DISEASES; BRAIN STEM disorders; SPINAL CORD DISEASES; and PERIPHERAL NERVOUS SYSTEM DISEASES. Manifestations include impairments of vegetative functions including the maintenance of BLOOD PRESSURE; HEART RATE; pupil function; SWEATING; REPRODUCTIVE AND URINARY PHYSIOLOGY; and DIGESTION.Cardiac Output, Low: A state of subnormal or depressed cardiac output at rest or during stress. It is a characteristic of CARDIOVASCULAR DISEASES, including congenital, valvular, rheumatic, hypertensive, coronary, and cardiomyopathic. The serious form of low cardiac output is characterized by marked reduction in STROKE VOLUME, and systemic vasoconstriction resulting in cold, pale, and sometimes cyanotic extremities.Anti-Arrhythmia Agents: Agents used for the treatment or prevention of cardiac arrhythmias. They may affect the polarization-repolarization phase of the action potential, its excitability or refractoriness, or impulse conduction or membrane responsiveness within cardiac fibers. Anti-arrhythmia agents are often classed into four main groups according to their mechanism of action: sodium channel blockade, beta-adrenergic blockade, repolarization prolongation, or calcium channel blockade.Prospective Studies: Observation of a population for a sufficient number of persons over a sufficient number of years to generate incidence or mortality rates subsequent to the selection of the study group.Myocytes, Cardiac: Striated muscle cells found in the heart. They are derived from cardiac myoblasts (MYOBLASTS, CARDIAC).Signal Processing, Computer-Assisted: Computer-assisted processing of electric, ultrasonic, or electronic signals to interpret function and activity.Supine Position: The posture of an individual lying face up.Systole: Period of contraction of the HEART, especially of the HEART VENTRICLES.Epinephrine: The active sympathomimetic hormone from the ADRENAL MEDULLA. It stimulates both the alpha- and beta- adrenergic systems, causes systemic VASOCONSTRICTION and gastrointestinal relaxation, stimulates the HEART, and dilates BRONCHI and cerebral vessels. It is used in ASTHMA and CARDIAC FAILURE and to delay absorption of local ANESTHETICS.Double-Blind Method: A method of studying a drug or procedure in which both the subjects and investigators are kept unaware of who is actually getting which specific treatment.Dose-Response Relationship, Drug: The relationship between the dose of an administered drug and the response of the organism to the drug.Diastole: Post-systolic relaxation of the HEART, especially the HEART VENTRICLES.Cardiomyopathy, Dilated: A form of CARDIAC MUSCLE disease that is characterized by ventricular dilation, VENTRICULAR DYSFUNCTION, and HEART FAILURE. Risk factors include SMOKING; ALCOHOL DRINKING; HYPERTENSION; INFECTION; PREGNANCY; and mutations in the LMNA gene encoding LAMIN TYPE A, a NUCLEAR LAMINA protein.Risk Factors: An aspect of personal behavior or lifestyle, environmental exposure, or inborn or inherited characteristic, which, on the basis of epidemiologic evidence, is known to be associated with a health-related condition considered important to prevent.Body Temperature: The measure of the level of heat of a human or animal.Atenolol: A cardioselective beta-1 adrenergic blocker possessing properties and potency similar to PROPRANOLOL, but without a negative inotropic effect.Regional Blood Flow: The flow of BLOOD through or around an organ or region of the body.Ventricular Dysfunction, Left: A condition in which the LEFT VENTRICLE of the heart was functionally impaired. This condition usually leads to HEART FAILURE; MYOCARDIAL INFARCTION; and other cardiovascular complications. Diagnosis is made by measuring the diminished ejection fraction and a depressed level of motility of the left ventricular wall.Reference Values: The range or frequency distribution of a measurement in a population (of organisms, organs or things) that has not been selected for the presence of disease or abnormality.Tilt-Table Test: A standard and widely accepted diagnostic test used to identify patients who have a vasodepressive and/or cardioinhibitory response as a cause of syncope. (From Braunwald, Heart Disease, 7th ed)Catecholamines: A general class of ortho-dihydroxyphenylalkylamines derived from tyrosine.Rats, Sprague-Dawley: A strain of albino rat used widely for experimental purposes because of its calmness and ease of handling. It was developed by the Sprague-Dawley Animal Company.Hypotension: Abnormally low BLOOD PRESSURE that can result in inadequate blood flow to the brain and other vital organs. Common symptom is DIZZINESS but greater negative impacts on the body occur when there is prolonged depravation of oxygen and nutrients.Phenylephrine: An alpha-1 adrenergic agonist used as a mydriatic, nasal decongestant, and cardiotonic agent.Rats, Wistar: A strain of albino rat developed at the Wistar Institute that has spread widely at other institutions. This has markedly diluted the original strain.Circadian Rhythm: The regular recurrence, in cycles of about 24 hours, of biological processes or activities, such as sensitivity to drugs and stimuli, hormone secretion, sleeping, and feeding.Follow-Up Studies: Studies in which individuals or populations are followed to assess the outcome of exposures, procedures, or effects of a characteristic, e.g., occurrence of disease.Cilia: Populations of thin, motile processes found covering the surface of ciliates (CILIOPHORA) or the free surface of the cells making up ciliated EPITHELIUM. Each cilium arises from a basic granule in the superficial layer of CYTOPLASM. The movement of cilia propels ciliates through the liquid in which they live. The movement of cilia on a ciliated epithelium serves to propel a surface layer of mucus or fluid. (King & Stansfield, A Dictionary of Genetics, 4th ed)Consciousness: Sense of awareness of self and of the environment.Anesthesia: A state characterized by loss of feeling or sensation. This depression of nerve function is usually the result of pharmacologic action and is induced to allow performance of surgery or other painful procedures.Atrial Premature Complexes: A type of cardiac arrhythmia with premature atrial contractions or beats caused by signals originating from ectopic atrial sites. The ectopic signals may or may not conduct to the HEART VENTRICLES. Atrial premature complexes are characterized by premature P waves on ECG which are different in configuration from the P waves generated by the normal pacemaker complex in the SINOATRIAL NODE.Fetal Monitoring: Physiologic or biochemical monitoring of the fetus. It is usually done during LABOR, OBSTETRIC and may be performed in conjunction with the monitoring of uterine activity. It may also be performed prenatally as when the mother is undergoing surgery.Pulse: The rhythmical expansion and contraction of an ARTERY produced by waves of pressure caused by the ejection of BLOOD from the left ventricle of the HEART as it contracts.Adrenergic beta-Agonists: Drugs that selectively bind to and activate beta-adrenergic receptors.Monitoring, Physiologic: The continuous measurement of physiological processes, blood pressure, heart rate, renal output, reflexes, respiration, etc., in a patient or experimental animal; includes pharmacologic monitoring, the measurement of administered drugs or their metabolites in the blood, tissues, or urine.Perfusion: Treatment process involving the injection of fluid into an organ or tissue.Cardiomegaly: Enlargement of the HEART, usually indicated by a cardiothoracic ratio above 0.50. Heart enlargement may involve the right, the left, or both HEART VENTRICLES or HEART ATRIA. Cardiomegaly is a nonspecific symptom seen in patients with chronic systolic heart failure (HEART FAILURE) or several forms of CARDIOMYOPATHIES.Pacemaker, Artificial: A device designed to stimulate, by electric impulses, contraction of the heart muscles. It may be temporary (external) or permanent (internal or internal-external).Cross-Over Studies: Studies comparing two or more treatments or interventions in which the subjects or patients, upon completion of the course of one treatment, are switched to another. In the case of two treatments, A and B, half the subjects are randomly allocated to receive these in the order A, B and half to receive them in the order B, A. A criticism of this design is that effects of the first treatment may carry over into the period when the second is given. (Last, A Dictionary of Epidemiology, 2d ed)Blood Flow Velocity: A value equal to the total volume flow divided by the cross-sectional area of the vascular bed.Atrioventricular Node: A small nodular mass of specialized muscle fibers located in the interatrial septum near the opening of the coronary sinus. It gives rise to the atrioventricular bundle of the conduction system of the heart.Diving: An activity in which the organism plunges into water. It includes scuba and bell diving. Diving as natural behavior of animals goes here, as well as diving in decompression experiments with humans or animals.Predictive Value of Tests: In screening and diagnostic tests, the probability that a person with a positive test is a true positive (i.e., has the disease), is referred to as the predictive value of a positive test; whereas, the predictive value of a negative test is the probability that the person with a negative test does not have the disease. Predictive value is related to the sensitivity and specificity of the test.Hypertension: Persistently high systemic arterial BLOOD PRESSURE. Based on multiple readings (BLOOD PRESSURE DETERMINATION), hypertension is currently defined as when SYSTOLIC PRESSURE is consistently greater than 140 mm Hg or when DIASTOLIC PRESSURE is consistently 90 mm Hg or more.Treatment Outcome: Evaluation undertaken to assess the results or consequences of management and procedures used in combating disease in order to determine the efficacy, effectiveness, safety, and practicability of these interventions in individual cases or series.Analysis of Variance: A statistical technique that isolates and assesses the contributions of categorical independent variables to variation in the mean of a continuous dependent variable.Oxygen: An element with atomic symbol O, atomic number 8, and atomic weight [15.99903; 15.99977]. It is the most abundant element on earth and essential for respiration.Myocardial Reperfusion Injury: Damage to the MYOCARDIUM resulting from MYOCARDIAL REPERFUSION (restoration of blood flow to ischemic areas of the HEART.) Reperfusion takes place when there is spontaneous thrombolysis, THROMBOLYTIC THERAPY, collateral flow from other coronary vascular beds, or reversal of vasospasm.Cardiomyopathies: A group of diseases in which the dominant feature is the involvement of the CARDIAC MUSCLE itself. Cardiomyopathies are classified according to their predominant pathophysiological features (DILATED CARDIOMYOPATHY; HYPERTROPHIC CARDIOMYOPATHY; RESTRICTIVE CARDIOMYOPATHY) or their etiological/pathological factors (CARDIOMYOPATHY, ALCOHOLIC; ENDOCARDIAL FIBROELASTOSIS).Atrial Fibrillation: Abnormal cardiac rhythm that is characterized by rapid, uncoordinated firing of electrical impulses in the upper chambers of the heart (HEART ATRIA). In such case, blood cannot be effectively pumped into the lower chambers of the heart (HEART VENTRICLES). It is caused by abnormal impulse generation.Disease Models, Animal: Naturally occurring or experimentally induced animal diseases with pathological processes sufficiently similar to those of human diseases. They are used as study models for human diseases.Benzazepines: Compounds with BENZENE fused to AZEPINES.Adrenergic beta-1 Receptor Antagonists: Drugs that bind to and block the activation of ADRENERGIC BETA-1 RECEPTORS.Ventricular Function: The hemodynamic and electrophysiological action of the HEART VENTRICLES.Valsalva Maneuver: Forced expiratory effort against a closed GLOTTIS.Rabbits: The species Oryctolagus cuniculus, in the family Leporidae, order LAGOMORPHA. Rabbits are born in burrows, furless, and with eyes and ears closed. In contrast with HARES, rabbits have 22 chromosome pairs.Atrial Function: The hemodynamic and electrophysiological action of the HEART ATRIA.Vasodilator Agents: Drugs used to cause dilation of the blood vessels.Heart Ventricles: The lower right and left chambers of the heart. The right ventricle pumps venous BLOOD into the LUNGS and the left ventricle pumps oxygenated blood into the systemic arterial circulation.Heart Arrest: Cessation of heart beat or MYOCARDIAL CONTRACTION. If it is treated within a few minutes, heart arrest can be reversed in most cases to normal cardiac rhythm and effective circulation.Energy Metabolism: The chemical reactions involved in the production and utilization of various forms of energy in cells.Heart Failure, Systolic: Heart failure caused by abnormal myocardial contraction during SYSTOLE leading to defective cardiac emptying.Chronic Disease: Diseases which have one or more of the following characteristics: they are permanent, leave residual disability, are caused by nonreversible pathological alteration, require special training of the patient for rehabilitation, or may be expected to require a long period of supervision, observation, or care. (Dictionary of Health Services Management, 2d ed)Coronary Circulation: The circulation of blood through the CORONARY VESSELS of the HEART.Ventricular Fibrillation: A potentially lethal cardiac arrhythmia that is characterized by uncoordinated extremely rapid firing of electrical impulses (400-600/min) in HEART VENTRICLES. Such asynchronous ventricular quivering or fibrillation prevents any effective cardiac output and results in unconsciousness (SYNCOPE). It is one of the major electrocardiographic patterns seen with CARDIAC ARREST.Heart Septum: This structure includes the thin muscular atrial septum between the two HEART ATRIA, and the thick muscular ventricular septum between the two HEART VENTRICLES.Ventricular Remodeling: The geometric and structural changes that the HEART VENTRICLES undergo, usually following MYOCARDIAL INFARCTION. It comprises expansion of the infarct and dilatation of the healthy ventricle segments. While most prevalent in the left ventricle, it can also occur in the right ventricle.Tachycardia, Ventricular: An abnormally rapid ventricular rhythm usually in excess of 150 beats per minute. It is generated within the ventricle below the BUNDLE OF HIS, either as autonomic impulse formation or reentrant impulse conduction. Depending on the etiology, onset of ventricular tachycardia can be paroxysmal (sudden) or nonparoxysmal, its wide QRS complexes can be uniform or polymorphic, and the ventricular beating may be independent of the atrial beating (AV dissociation).Physical Endurance: The time span between the beginning of physical activity by an individual and the termination because of exhaustion.Death, Sudden, Cardiac: Unexpected rapid natural death due to cardiovascular collapse within one hour of initial symptoms. It is usually caused by the worsening of existing heart diseases. The sudden onset of symptoms, such as CHEST PAIN and CARDIAC ARRHYTHMIAS, particularly VENTRICULAR TACHYCARDIA, can lead to the loss of consciousness and cardiac arrest followed by biological death. (from Braunwald's Heart Disease: A Textbook of Cardiovascular Medicine, 7th ed., 2005)Autonomic Nerve Block: Interruption of sympathetic pathways, by local injection of an anesthetic agent, at any of four levels: peripheral nerve block, sympathetic ganglion block, extradural block, and subarachnoid block.Antihypertensive Agents: Drugs used in the treatment of acute or chronic vascular HYPERTENSION regardless of pharmacological mechanism. Among the antihypertensive agents are DIURETICS; (especially DIURETICS, THIAZIDE); ADRENERGIC BETA-ANTAGONISTS; ADRENERGIC ALPHA-ANTAGONISTS; ANGIOTENSIN-CONVERTING ENZYME INHIBITORS; CALCIUM CHANNEL BLOCKERS; GANGLIONIC BLOCKERS; and VASODILATOR AGENTS.Receptors, Adrenergic, beta: One of two major pharmacologically defined classes of adrenergic receptors. The beta adrenergic receptors play an important role in regulating CARDIAC MUSCLE contraction, SMOOTH MUSCLE relaxation, and GLYCOGENOLYSIS.Heart, Artificial: A pumping mechanism that duplicates the output, rate, and blood pressure of the natural heart. It may replace the function of the entire heart or a portion of it, and may be an intracorporeal, extracorporeal, or paracorporeal heart. (Dorland, 28th ed)Echocardiography, Doppler: Measurement of intracardiac blood flow using an M-mode and/or two-dimensional (2-D) echocardiogram while simultaneously recording the spectrum of the audible Doppler signal (e.g., velocity, direction, amplitude, intensity, timing) reflected from the moving column of red blood cells.Sympathomimetics: Drugs that mimic the effects of stimulating postganglionic adrenergic sympathetic nerves. Included here are drugs that directly stimulate adrenergic receptors and drugs that act indirectly by provoking the release of adrenergic transmitters.Anoxia: Relatively complete absence of oxygen in one or more tissues.Clonidine: An imidazoline sympatholytic agent that stimulates ALPHA-2 ADRENERGIC RECEPTORS and central IMIDAZOLINE RECEPTORS. It is commonly used in the management of HYPERTENSION.Sympatholytics: Drugs that inhibit the actions of the sympathetic nervous system by any mechanism. The most common of these are the ADRENERGIC ANTAGONISTS and drugs that deplete norepinephrine or reduce the release of transmitters from adrenergic postganglionic terminals (see ADRENERGIC AGENTS). Drugs that act in the central nervous system to reduce sympathetic activity (e.g., centrally acting alpha-2 adrenergic agonists, see ADRENERGIC ALPHA-AGONISTS) are included here.Ventricular Pressure: The pressure within a CARDIAC VENTRICLE. Ventricular pressure waveforms can be measured in the beating heart by catheterization or estimated using imaging techniques (e.g., DOPPLER ECHOCARDIOGRAPHY). The information is useful in evaluating the function of the MYOCARDIUM; CARDIAC VALVES; and PERICARDIUM, particularly with simultaneous measurement of other (e.g., aortic or atrial) pressures.Cardiac Volume: The volume of the HEART, usually relating to the volume of BLOOD contained within it at various periods of the cardiac cycle. The amount of blood ejected from a ventricle at each beat is STROKE VOLUME.Reproducibility of Results: The statistical reproducibility of measurements (often in a clinical context), including the testing of instrumentation or techniques to obtain reproducible results. The concept includes reproducibility of physiological measurements, which may be used to develop rules to assess probability or prognosis, or response to a stimulus; reproducibility of occurrence of a condition; and reproducibility of experimental results.Heart Valve Prosthesis: A device that substitutes for a heart valve. It may be composed of biological material (BIOPROSTHESIS) and/or synthetic material.Heart Injuries: General or unspecified injuries to the heart.Cardiovascular Diseases: Pathological conditions involving the CARDIOVASCULAR SYSTEM including the HEART; the BLOOD VESSELS; or the PERICARDIUM.Action Potentials: Abrupt changes in the membrane potential that sweep along the CELL MEMBRANE of excitable cells in response to excitation stimuli.Aging: The gradual irreversible changes in structure and function of an organism that occur as a result of the passage of time.Prognosis: A prediction of the probable outcome of a disease based on a individual's condition and the usual course of the disease as seen in similar situations.Anesthesia, General: Procedure in which patients are induced into an unconscious state through use of various medications so that they do not feel pain during surgery.Respiratory Mechanics: The physical or mechanical action of the LUNGS; DIAPHRAGM; RIBS; and CHEST WALL during respiration. It includes airflow, lung volume, neural and reflex controls, mechanoreceptors, breathing patterns, etc.Injections, Intravenous: Injections made into a vein for therapeutic or experimental purposes.Age Factors: Age as a constituent element or influence contributing to the production of a result. It may be applicable to the cause or the effect of a circumstance. It is used with human or animal concepts but should be differentiated from AGING, a physiological process, and TIME FACTORS which refers only to the passage of time.Nitroprusside: A powerful vasodilator used in emergencies to lower blood pressure or to improve cardiac function. It is also an indicator for free sulfhydryl groups in proteins.Respiratory Rate: The number of times an organism breathes with the lungs (RESPIRATION) per unit time, usually per minute.Tachycardia, Sinus: Simple rapid heartbeats caused by rapid discharge of impulses from the SINOATRIAL NODE, usually between 100 and 180 beats/min in adults. It is characterized by a gradual onset and termination. Sinus tachycardia is common in infants, young children, and adults during strenuous physical activities.Body Weight: The mass or quantity of heaviness of an individual. It is expressed by units of pounds or kilograms.Glycopyrrolate: A muscarinic antagonist used as an antispasmodic, in some disorders of the gastrointestinal tract, and to reduce salivation with some anesthetics.Rheumatic Heart Disease: Cardiac manifestation of systemic rheumatological conditions, such as RHEUMATIC FEVER. Rheumatic heart disease can involve any part the heart, most often the HEART VALVES and the ENDOCARDIUM.Parasympatholytics: Agents that inhibit the actions of the parasympathetic nervous system. The major group of drugs used therapeutically for this purpose is the MUSCARINIC ANTAGONISTS.Infusions, Intravenous: The long-term (minutes to hours) administration of a fluid into the vein through venipuncture, either by letting the fluid flow by gravity or by pumping it.Dobutamine: A catecholamine derivative with specificity for BETA-1 ADRENERGIC RECEPTORS. It is commonly used as a cardiotonic agent after CARDIAC SURGERY and during DOBUTAMINE STRESS ECHOCARDIOGRAPHY.Digoxin: A cardiotonic glycoside obtained mainly from Digitalis lanata; it consists of three sugars and the aglycone DIGOXIGENIN. Digoxin has positive inotropic and negative chronotropic activity. It is used to control ventricular rate in ATRIAL FIBRILLATION and in the management of congestive heart failure with atrial fibrillation. Its use in congestive heart failure and sinus rhythm is less certain. The margin between toxic and therapeutic doses is small. (From Martindale, The Extra Pharmacopoeia, 30th ed, p666)Physical Conditioning, Animal: Diet modification and physical exercise to improve the ability of animals to perform physical activities.Blood Circulation: The movement of the BLOOD as it is pumped through the CARDIOVASCULAR SYSTEM.Electric Stimulation: Use of electric potential or currents to elicit biological responses.Carbon Dioxide: A colorless, odorless gas that can be formed by the body and is necessary for the respiration cycle of plants and animals.Blood Volume: Volume of circulating BLOOD. It is the sum of the PLASMA VOLUME and ERYTHROCYTE VOLUME.Rats, Inbred SHR: A strain of Rattus norvegicus with elevated blood pressure used as a model for studying hypertension and stroke.Muscle, Skeletal: A subtype of striated muscle, attached by TENDONS to the SKELETON. Skeletal muscles are innervated and their movement can be consciously controlled. They are also called voluntary muscles.Arterial Pressure: The blood pressure in the ARTERIES. It is commonly measured with a SPHYGMOMANOMETER on the upper arm which represents the arterial pressure in the BRACHIAL ARTERY.Calcium: A basic element found in nearly all organized tissues. It is a member of the alkaline earth family of metals with the atomic symbol Ca, atomic number 20, and atomic weight 40. Calcium is the most abundant mineral in the body and combines with phosphorus to form calcium phosphate in the bones and teeth. It is essential for the normal functioning of nerves and muscles and plays a role in blood coagulation (as factor IV) and in many enzymatic processes.Muscarinic Antagonists: Drugs that bind to but do not activate MUSCARINIC RECEPTORS, thereby blocking the actions of endogenous ACETYLCHOLINE or exogenous agonists. Muscarinic antagonists have widespread effects including actions on the iris and ciliary muscle of the eye, the heart and blood vessels, secretions of the respiratory tract, GI system, and salivary glands, GI motility, urinary bladder tone, and the central nervous system.Cardiotocography: Monitoring of FETAL HEART frequency before birth in order to assess impending prematurity in relation to the pattern or intensity of antepartum UTERINE CONTRACTION.Carotid Sinus: The dilated portion of the common carotid artery at its bifurcation into external and internal carotids. It contains baroreceptors which, when stimulated, cause slowing of the heart, vasodilatation, and a fall in blood pressure.Denervation: The resection or removal of the nerve to an organ or part. (Dorland, 28th ed)Vagotomy: The interruption or removal of any part of the vagus (10th cranial) nerve. Vagotomy may be performed for research or for therapeutic purposes.Nitroglycerin: A volatile vasodilator which relieves ANGINA PECTORIS by stimulating GUANYLATE CYCLASE and lowering cytosolic calcium. It is also sometimes used for TOCOLYSIS and explosives.Forearm: Part of the arm in humans and primates extending from the ELBOW to the WRIST.Risk Assessment: The qualitative or quantitative estimation of the likelihood of adverse effects that may result from exposure to specified health hazards or from the absence of beneficial influences. (Last, Dictionary of Epidemiology, 1988)Regression Analysis: Procedures for finding the mathematical function which best describes the relationship between a dependent variable and one or more independent variables. In linear regression (see LINEAR MODELS) the relationship is constrained to be a straight line and LEAST-SQUARES ANALYSIS is used to determine the best fit. In logistic regression (see LOGISTIC MODELS) the dependent variable is qualitative rather than continuously variable and LIKELIHOOD FUNCTIONS are used to find the best relationship. In multiple regression, the dependent variable is considered to depend on more than a single independent variable.Cold Temperature: An absence of warmth or heat or a temperature notably below an accustomed norm.Practolol: A beta-1 adrenergic antagonist that has been used in the emergency treatment of CARDIAC ARRYTHMIAS.Cardiac Catheterization: Procedures in which placement of CARDIAC CATHETERS is performed for therapeutic or diagnostic procedures.Physical Fitness: The ability to carry out daily tasks and perform physical activities in a highly functional state, often as a result of physical conditioning.Running: An activity in which the body is propelled by moving the legs rapidly. Running is performed at a moderate to rapid pace and should be differentiated from JOGGING, which is performed at a much slower pace.Natriuretic Peptide, Brain: A PEPTIDE that is secreted by the BRAIN and the HEART ATRIA, stored mainly in cardiac ventricular MYOCARDIUM. It can cause NATRIURESIS; DIURESIS; VASODILATION; and inhibits secretion of RENIN and ALDOSTERONE. It improves heart function. It contains 32 AMINO ACIDS.Kidney: Body organ that filters blood for the secretion of URINE and that regulates ion concentrations.Heart Failure, Diastolic: Heart failure caused by abnormal myocardial relaxation during DIASTOLE leading to defective cardiac filling.Hypotension, Orthostatic: A significant drop in BLOOD PRESSURE after assuming a standing position. Orthostatic hypotension is a finding, and defined as a 20-mm Hg decrease in systolic pressure or a 10-mm Hg decrease in diastolic pressure 3 minutes after the person has risen from supine to standing. Symptoms generally include DIZZINESS, blurred vision, and SYNCOPE.Renin: A highly specific (Leu-Leu) endopeptidase that generates ANGIOTENSIN I from its precursor ANGIOTENSINOGEN, leading to a cascade of reactions which elevate BLOOD PRESSURE and increase sodium retention by the kidney in the RENIN-ANGIOTENSIN SYSTEM. The enzyme was formerly listed as EC 3.4.99.19.Endocardium: The innermost layer of the heart, comprised of endothelial cells.Long QT Syndrome: A condition that is characterized by episodes of fainting (SYNCOPE) and varying degree of ventricular arrhythmia as indicated by the prolonged QT interval. The inherited forms are caused by mutation of genes encoding cardiac ion channel proteins. The two major forms are ROMANO-WARD SYNDROME and JERVELL-LANGE NIELSEN SYNDROME.Stress, Physiological: The unfavorable effect of environmental factors (stressors) on the physiological functions of an organism. Prolonged unresolved physiological stress can affect HOMEOSTASIS of the organism, and may lead to damaging or pathological conditions.American Heart Association: A voluntary organization concerned with the prevention and treatment of heart and vascular diseases.Anaerobic Threshold: The oxygen consumption level above which aerobic energy production is supplemented by anaerobic mechanisms during exercise, resulting in a sustained increase in lactate concentration and metabolic acidosis. The anaerobic threshold is affected by factors that modify oxygen delivery to the tissues; it is low in patients with heart disease. Methods of measurement include direct measure of lactate concentration, direct measurement of bicarbonate concentration, and gas exchange measurements.Syncope: A transient loss of consciousness and postural tone caused by diminished blood flow to the brain (i.e., BRAIN ISCHEMIA). Presyncope refers to the sensation of lightheadedness and loss of strength that precedes a syncopal event or accompanies an incomplete syncope. (From Adams et al., Principles of Neurology, 6th ed, pp367-9)Vagus Nerve: The 10th cranial nerve. The vagus is a mixed nerve which contains somatic afferents (from skin in back of the ear and the external auditory meatus), visceral afferents (from the pharynx, larynx, thorax, and abdomen), parasympathetic efferents (to the thorax and abdomen), and efferents to striated muscle (of the larynx and pharynx).Stress, Psychological: Stress wherein emotional factors predominate.Lactic Acid: A normal intermediate in the fermentation (oxidation, metabolism) of sugar. The concentrated form is used internally to prevent gastrointestinal fermentation. (From Stedman, 26th ed)Hypertrophy, Left Ventricular: Enlargement of the LEFT VENTRICLE of the heart. This increase in ventricular mass is attributed to sustained abnormal pressure or volume loads and is a contributor to cardiovascular morbidity and mortality.Adrenergic alpha-Agonists: Drugs that selectively bind to and activate alpha adrenergic receptors.
  • These sounds in these musical tracks are presented through monaural beats, binaural beats, isochronic tones, or a mixture involving combinations of all three of these modalities, described in detail below. (brainwaveentrainmentmp3.com)
  • That's why I decided to check out the Instant Heart Rate to find out if Android phones can be trusted with our health. (androidpit.com)
  • Yesterday, when I was browsing in health and fitness section of Android Marketplace I found an application which captures your heart beat rate (HBR) through phone without the use of any external hardware requirement. (blogspot.com)
  • Similar thresholds had been adopted by the American Heart Association for adults who are 18 years and older, but in November 2017 the American Heart Association announced revised definitions for blood pressure categories that increased the number of people considered to have high blood pressure. (wikipedia.org)
  • The aim of this study was to determine the association between HRT and HRV parameters and the relationship between HRT parameters and heart rate and number of ventricular premature beats (VPBs) used to calculate HRT parameters. (ovid.com)
  • 1. Disorders of the autonomic nervous system are frequently diagnosed by measuring heart rate changes in response to deep-breathing and lying-to-standing manoeuvres. (portlandpress.com)
  • Knowing your heart rate zone reminds you to maintain a proper level of exercise intensity. (harvard.edu)
  • A good way to maintain your level of moderate intensity is with heart rate training, where you exercise at 60% to 75% of your maximum heart rate. (harvard.edu)
  • Starting an exercise session with an aerobic warm-up and moving up to higher exercise levels reduces initial stress to muscles, including the heart, according to Duane Knudson, kinesiology professor at California State University, Chico. (livestrong.com)
  • Heart rate data can be really useful whether you're designing an exercise routine, studying your activity or anxiety levels or just want your shirt to blink with your heart beat. (com.pk)
  • Idiopathic inflammatory myopathies involve skeletal muscles and can be associated with interstitial lung disease and/or heart dysfunction, which may reduce exercise capacity. (springer.com)
  • In conclusion, impaired DLCO due to interstitial lung disease was suggested to be a fundamental parameter affecting exercise capacity, in addition to heart involvement, in patients with idiopathic inflammatory myopathies. (springer.com)
  • Use Heart rate app for optimizing your exercise and to track your progress. (cnet.com)
  • Turbo Beat classes provide the equipment, structured workouts and motivation to help you maximize intense fitness efforts. (eventbrite.co.uk)
  • With customised heart rate and motion monitoring, you can more accurately track your calorie burn during your toughest interval training workouts. (apple.com)
  • Take control of your goals by using ChargeHR to record your workouts and track all-day activity like heart rate, steps, distance, calories burned, stairs climbed and active minutes. (fitbit.com)
  • Faster the heart beats more will be the pressure with which blood circulates. (healthcaremagic.com)
  • It delivers small electrical impulse which stimulates the heart to beat faster when it is going too slow. (heart-disease-treatments.com)
  • Working out in hot conditions can result in making it easier to maintain a faster pace and cause perceived exertion to drop, higher blood plasma volume, increased sweat rate, decrease in salt in sweat, reduced heart rate at a given pace and temperature, and a quicker onset of sweating but these changes are noticeable only after about 2 weeks of heat exposure. (nowfoods.com)
  • A baby girl's heart rate is usually faster than a boy's, but only after the onset of labor. (kidshealth.org)
  • mean age 62 years) with coronary artery disease, a 24-hour ECG Holter monitoring was performed to calculate mean heart rate (RR interval), number of VPBs, time- and frequency-domain HRV parameters and two HRT parameters: turbulence onset (TO) and turbulence slope (TS). (ovid.com)
  • Calculate your desired target heart rate zone - the level at which your heart is being exercised and conditioned but not overworked. (shanrentech.com)
  • Also, remember that if you're not able to carry on a conversation at any time while exercising, the intensity may be too much, no matter what your optimal heart rate zone," says Dr. Baggish. (harvard.edu)
  • If you have difficulty staying in your zone for 30 minutes, do intervals: Slow your pace for a few minutes, and then increase the intensity until you reach your target heart rate zone again. (harvard.edu)