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.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.Heart: The hollow, muscular organ that maintains the circulation of the blood.Heart Rate: The number of times the HEART VENTRICLES contract per unit of time, usually per minute.Cerebral Ventricles: Four CSF-filled (see CEREBROSPINAL FLUID) cavities within the cerebral hemispheres (LATERAL VENTRICLES), in the midline (THIRD VENTRICLE) and within the PONS and MEDULLA OBLONGATA (FOURTH VENTRICLE).Third Ventricle: A narrow cleft inferior to the CORPUS CALLOSUM, within the DIENCEPHALON, between the paired thalami. Its floor is formed by the HYPOTHALAMUS, its anterior wall by the lamina terminalis, and its roof by EPENDYMA. It communicates with the FOURTH VENTRICLE by the CEREBRAL AQUEDUCT, and with the LATERAL VENTRICLES by the interventricular foramina.Fourth Ventricle: An irregularly shaped cavity in the RHOMBENCEPHALON, located between the MEDULLA OBLONGATA; the PONS; and the isthmus in front, and the CEREBELLUM behind. It is continuous with the central canal of the cord below and with the CEREBRAL AQUEDUCT above, and through its lateral and median apertures it communicates with the SUBARACHNOID SPACE.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.Lateral Ventricles: Cavity in each of the CEREBRAL HEMISPHERES derived from the cavity of the embryonic NEURAL TUBE. They are separated from each other by the SEPTUM PELLUCIDUM, and each communicates with the THIRD VENTRICLE by the foramen of Monro, through which also the choroid plexuses (CHOROID PLEXUS) of the lateral ventricles become continuous with that of the third ventricle.Heart Defects, Congenital: Developmental abnormalities involving structures of the heart. These defects are present at birth but may be discovered later in life.Cerebral Ventricle Neoplasms: Neoplasms located in the brain ventricles, including the two lateral, the third, and the fourth ventricle. Ventricular tumors may be primary (e.g., CHOROID PLEXUS NEOPLASMS and GLIOMA, SUBEPENDYMAL), metastasize from distant organs, or occur as extensions of locally invasive tumors from adjacent brain structures.Heart Diseases: Pathological conditions involving the HEART including its structural and functional abnormalities.Heart Transplantation: The transference of a heart from one human or animal to another.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.Heart Atria: The chambers of the heart, to which the BLOOD returns from the circulation.Myocardial Contraction: Contractile activity of the MYOCARDIUM.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.Ventricular Function: The hemodynamic and electrophysiological action of the HEART VENTRICLES.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.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.Echocardiography: Ultrasonic recording of the size, motion, and composition of the heart and surrounding tissues. The standard approach is transthoracic.Hemodynamics: The movement and the forces involved in the movement of the blood through the CARDIOVASCULAR SYSTEM.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 Function Tests: Examinations used to diagnose and treat heart conditions.Myocytes, Cardiac: Striated muscle cells found in the heart. They are derived from cardiac myoblasts (MYOBLASTS, CARDIAC).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.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.Endocardium: The innermost layer of the heart, comprised of endothelial cells.Ventricular Function, Right: The hemodynamic and electrophysiological action of the right HEART VENTRICLE.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.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).Encyclopedias as Topic: Works containing information articles on subjects in every field of knowledge, usually arranged in alphabetical order, or a similar work limited to a special field or subject. (From The ALA Glossary of Library and Information Science, 1983)Chordae Tendineae: The tendinous cords that connect each cusp of the two atrioventricular HEART VALVES to appropriate PAPILLARY MUSCLES in the HEART VENTRICLES, preventing the valves from reversing themselves when the ventricles contract.Truncus Arteriosus: The arterial trunk arising from the fetal heart. During development, it divides into AORTA and the PULMONARY ARTERY.Tricuspid Valve: The valve consisting of three cusps situated between the right atrium and right ventricle of the heart.Mitral Valve: The valve between the left atrium and left ventricle of the heart.Heart Murmurs: Heart sounds caused by vibrations resulting from the flow of blood through the heart. Heart murmurs can be examined by HEART AUSCULTATION, and analyzed by their intensity (6 grades), duration, timing (systolic, diastolic, or continuous), location, transmission, and quality (musical, vibratory, blowing, etc).Heart Auscultation: Act of listening for sounds within the heart.Phonocardiography: Graphic registration of the heart sounds picked up as vibrations and transformed by a piezoelectric crystal microphone into a varying electrical output according to the stresses imposed by the sound waves. The electrical output is amplified by a stethograph amplifier and recorded by a device incorporated into the electrocardiograph or by a multichannel recording machine.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.Blalock-Taussig Procedure: A cardiovascular procedure performed to create a blood supply to the PULMONARY CIRCULATION. It involves making a connection between the subclavian, or carotid branch of the AORTA, or the AORTIC ARCH to the PULMONARY ARTERY.Fontan Procedure: A procedure in which total right atrial or total caval blood flow is channeled directly into the pulmonary artery or into a small right ventricle that serves only as a conduit. The principal congenital malformations for which this operation is useful are TRICUSPID ATRESIA and single ventricle with pulmonary stenosis.Norwood Procedures: A set of surgical procedures performed to establish sufficient outflow to the systemic circulation in individuals with univentricular congenital heart malformations, such as HYPOPLASTIC LEFT HEART SYNDROME, and MITRAL VALVE atresia, associated with systemic outflow obstruction. Follow-on surgeries may be performed and consist of a HEMI-FONTAN PROCEDURE as the stage 2 Norwood procedure and a FONTAN PROCEDURE as the stage 3 Norwood procedure.PhiladelphiaHeart Bypass, Right: Diversion of the flow of blood from the entrance to the right atrium directly to the pulmonary arteries, avoiding the right atrium and right ventricle (Dorland, 28th ed). This a permanent procedure often performed to bypass a congenitally deformed right atrium or right ventricle.Tricuspid Valve Insufficiency: Backflow of blood from the RIGHT VENTRICLE into the RIGHT ATRIUM due to imperfect closure of the TRICUSPID VALVE.Papillary Muscles: Conical muscular projections from the walls of the cardiac ventricles, attached to the cusps of the atrioventricular valves by the chordae tendineae.Muscle Contraction: A process leading to shortening and/or development of tension in muscle tissue. Muscle contraction occurs by a sliding filament mechanism whereby actin filaments slide inward among the myosin filaments.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.Tricuspid Valve Stenosis: The pathologic narrowing of the orifice of the TRICUSPID VALVE. This hinders the emptying of RIGHT ATRIUM leading to elevated right atrial pressure and systemic venous congestion. Tricuspid valve stenosis is almost always due to RHEUMATIC FEVER.Antarctic Regions: The continent lying around the South Pole and the southern waters of the Atlantic, Pacific, and Indian Oceans. It includes the Falkland Islands Dependencies. (From Webster's New Geographical Dictionary, 1988, p55)Myoglobin: A conjugated protein which is the oxygen-transporting pigment of muscle. It is made up of one globin polypeptide chain and one heme group.Perciformes: The most diversified of all fish orders and the largest vertebrate order. It includes many of the commonly known fish such as porgies, croakers, sunfishes, dolphin fish, mackerels, TUNA, etc.Biology: One of the BIOLOGICAL SCIENCE DISCIPLINES concerned with the origin, structure, development, growth, function, genetics, and reproduction of animals, plants, and microorganisms.Fishes: A group of cold-blooded, aquatic vertebrates having gills, fins, a cartilaginous or bony endoskeleton, and elongated bodies covered with scales.Seals, Earless: The family Phocidae, suborder PINNIPEDIA, order CARNIVORA, comprising the true seals. They lack external ears and are unable to use their hind flippers to walk. It includes over 18 species including the harp seal, probably the best known seal species in the world.