Femoral Vein: The vein accompanying the femoral artery in the same sheath; it is a continuation of the popliteal vein and becomes the external iliac vein.Veins: The vessels carrying blood away from the capillary beds.Phlebography: Radiographic visualization or recording of a vein after the injection of contrast medium.May-Thurner Syndrome: A compression of ILIAC VEIN that results in a decreased flow in the vein and in the left LOWER EXTREMITY due to a vascular malformation. It may result in left leg EDEMA, pain, iliofemoral DEEP VENOUS THROMBOSIS and POSTTHROMBOTIC SYNDROME. Compression of the left common ILIAC VEIN by the right common ILIAC ARTERY against the underlying fifth LUMBAR VERTEBRA is the typical underlying malformation.Venous Thrombosis: The formation or presence of a blood clot (THROMBUS) within a vein.Vena Cava, Inferior: The venous trunk which receives blood from the lower extremities and from the pelvic and abdominal organs.Constriction, Pathologic: The condition of an anatomical structure's being constricted beyond normal dimensions.Saphenous Vein: The vein which drains the foot and leg.Ureterostomy: Surgical formation of an opening in the ureter for external drainage of the urine; cutaneous route utilizes a ureteral orifice emerging through the skin.Portal Vein: A short thick vein formed by union of the superior mesenteric vein and the splenic vein.Varicose Veins: Enlarged and tortuous VEINS.Mesenteric Veins: Veins which return blood from the intestines; the inferior mesenteric vein empties into the splenic vein, the superior mesenteric vein joins the splenic vein to form the portal vein.Klippel-Trenaunay-Weber Syndrome: A congenital disorder that is characterized by a triad of capillary malformations (HEMANGIOMA), venous malformations (ARTERIOVENOUS FISTULA), and soft tissue or bony hypertrophy of the limb. This syndrome is caused by mutations in the VG5Q gene which encodes a strong angiogenesis stimulator.Iliac Artery: Either of two large arteries originating from the abdominal aorta; they supply blood to the pelvis, abdominal wall and legs.Peripheral Vascular Diseases: Pathological processes involving any one of the BLOOD VESSELS in the vasculature outside the HEART.Pulmonary Veins: The veins that return the oxygenated blood from the lungs to the left atrium of the heart.Thrombectomy: Surgical removal of an obstructing clot or foreign material from a blood vessel at the point of its formation. Removal of a clot arising from a distant site is called EMBOLECTOMY.Vascular Neoplasms: Neoplasms located in the vasculature system, such as ARTERIES and VEINS. They are differentiated from neoplasms of vascular tissue (NEOPLASMS, VASCULAR TISSUE), such as ANGIOFIBROMA or HEMANGIOMA.Jugular Veins: Veins in the neck which drain the brain, face, and neck into the brachiocephalic or subclavian veins.Postthrombotic Syndrome: A condition caused by one or more episodes of DEEP VEIN THROMBOSIS, usually the blood clots are lodged in the legs. Clinical features include EDEMA; PAIN; aching; heaviness; and MUSCLE CRAMP in the leg. When severe leg swelling leads to skin breakdown, it is called venous STASIS ULCER.Iliac Vein: A vein on either side of the body which is formed by the union of the external and internal iliac veins and passes upward to join with its fellow of the opposite side to form the inferior vena cava.Vena Cava Filters: Mechanical devices inserted in the inferior vena cava that prevent the migration of blood clots from deep venous thrombosis of the leg.Vascular Diseases: Pathological processes involving any of the BLOOD VESSELS in the cardiac or peripheral circulation. They include diseases of ARTERIES; VEINS; and rest of the vasculature system in the body.Varicose Ulcer: Skin breakdown or ulceration caused by VARICOSE VEINS in which there is too much hydrostatic pressure in the superficial venous system of the leg. Venous hypertension leads to increased pressure in the capillary bed, transudation of fluid and proteins into the interstitial space, altering blood flow and supply of nutrients to the skin and subcutaneous tissues, and eventual ulceration.Venous Insufficiency: Impaired venous blood flow or venous return (venous stasis), usually caused by inadequate venous valves. Venous insufficiency often occurs in the legs, and is associated with EDEMA and sometimes with VENOUS STASIS ULCERS at the ankle.Vascular Patency: The degree to which BLOOD VESSELS are not blocked or obstructed.Rupture, Spontaneous: Tear or break of an organ, vessel or other soft part of the body, occurring in the absence of external force.Ultrasonography, Doppler, Duplex: Ultrasonography applying the Doppler effect combined with real-time imaging. The real-time image is created by rapid movement of the ultrasound beam. A powerful advantage of this technique is the ability to estimate the velocity of flow from the Doppler shift frequency.Catheterization, Peripheral: Insertion of a catheter into a peripheral artery, vein, or airway for diagnostic or therapeutic purposes.Stents: Devices that provide support for tubular structures that are being anastomosed or for body cavities during skin grafting.Renal Veins: Short thick veins which return blood from the kidneys to the vena cava.Vascular Surgical Procedures: Operative procedures for the treatment of vascular disorders.Umbilical Veins: Venous vessels in the umbilical cord. They carry oxygenated, nutrient-rich blood from the mother to the FETUS via the PLACENTA. In humans, there is normally one umbilical vein.Arteriovenous Fistula: An abnormal direct communication between an artery and a vein without passing through the CAPILLARIES. An A-V fistula usually leads to the formation of a dilated sac-like connection, arteriovenous aneurysm. The locations and size of the shunts determine the degree of effects on the cardiovascular functions such as BLOOD PRESSURE and HEART RATE.Edema: Abnormal fluid accumulation in TISSUES or body cavities. Most cases of edema are present under the SKIN in SUBCUTANEOUS TISSUE.Iatrogenic Disease: Any adverse condition in a patient occurring as the result of treatment by a physician, surgeon, or other health professional, especially infections acquired by a patient during the course of treatment.Pelvis: The space or compartment surrounded by the pelvic girdle (bony pelvis). It is subdivided into the greater pelvis and LESSER PELVIS. The pelvic girdle is formed by the PELVIC BONES and SACRUM.Tomography, X-Ray Computed: Tomography using x-ray transmission and a computer algorithm to reconstruct the image.Hepatic Veins: Veins which drain the liver.Popliteal Vein: The vein formed by the union of the anterior and posterior tibial veins; it courses through the popliteal space and becomes the femoral vein.Ultrasonography, Interventional: The use of ultrasound to guide minimally invasive surgical procedures such as needle ASPIRATION BIOPSY; DRAINAGE; etc. Its widest application is intravascular ultrasound imaging but it is useful also in urology and intra-abdominal conditions.Wounds, Gunshot: Disruption of structural continuity of the body as a result of the discharge of firearms.Retroperitoneal Space: An area occupying the most posterior aspect of the ABDOMINAL CAVITY. It is bounded laterally by the borders of the quadratus lumborum muscles and extends from the DIAPHRAGM to the brim of the true PELVIS, where it continues as the pelvic extraperitoneal space.Pulmonary Embolism: Blocking of the PULMONARY ARTERY or one of its branches by an EMBOLUS.Anticoagulants: Agents that prevent clotting.Arteriovenous Shunt, Surgical: Surgical shunt allowing direct passage of blood from an artery to a vein. (From Dorland, 28th ed)Angioplasty, Balloon: Use of a balloon catheter for dilation of an occluded artery. It is used in treatment of arterial occlusive diseases, including renal artery stenosis and arterial occlusions in the leg. For the specific technique of BALLOON DILATION in coronary arteries, ANGIOPLASTY, BALLOON, CORONARY is available.Subclavian Vein: The continuation of the axillary vein which follows the subclavian artery and then joins the internal jugular vein to form the brachiocephalic vein.Anastomosis, Surgical: Surgical union or shunt between ducts, tubes or vessels. It may be end-to-end, end-to-side, side-to-end, or side-to-side.Leg: The inferior part of the lower extremity between the KNEE and the ANKLE.Splenic Vein: Vein formed by the union (at the hilus of the spleen) of several small veins from the stomach, pancreas, spleen and mesentery.Cerebral Veins: Veins draining the cerebrum.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.Catheterization: Use or insertion of a tubular device into a duct, blood vessel, hollow organ, or body cavity for injecting or withdrawing fluids for diagnostic or therapeutic purposes. It differs from INTUBATION in that the tube here is used to restore or maintain patency in obstructions.Lower Extremity: The region of the lower limb in animals, extending from the gluteal region to the FOOT, and including the BUTTOCKS; HIP; and LEG.Retinal Vein: Central retinal vein and its tributaries. It runs a short course within the optic nerve and then leaves and empties into the superior ophthalmic vein or cavernous sinus.Ultrasonography, Doppler, Color: Ultrasonography applying the Doppler effect, with the superposition of flow information as colors on a gray scale in a real-time image. This type of ultrasonography is well-suited to identifying the location of high-velocity flow (such as in a stenosis) or of mapping the extent of flow in a certain region.Blood Vessel Prosthesis Implantation: Surgical insertion of BLOOD VESSEL PROSTHESES to repair injured or diseased blood vessels.Ligation: Application of a ligature to tie a vessel or strangulate a part.Azygos Vein: A vein which arises from the right ascending lumbar vein or the vena cava, enters the thorax through the aortic orifice in the diaphragm, and terminates in the superior vena cava.Brachiocephalic Veins: Large veins on either side of the root of the neck formed by the junction of the internal jugular and subclavian veins. They drain blood from the head, neck, and upper extremities, and unite to form the superior vena cava.Thrombolytic Therapy: Use of infusions of FIBRINOLYTIC AGENTS to destroy or dissolve thrombi in blood vessels or bypass grafts.Polytetrafluoroethylene: Homopolymer of tetrafluoroethylene. Nonflammable, tough, inert plastic tubing or sheeting; used to line vessels, insulate, protect or lubricate apparatus; also as filter, coating for surgical implants or as prosthetic material. Synonyms: Fluoroflex; Fluoroplast; Ftoroplast; Halon; Polyfene; PTFE; Tetron.Thrombosis: Formation and development of a thrombus or blood clot in the blood vessel.Axillary Vein: The venous trunk of the upper limb; a continuation of the basilar and brachial veins running from the lower border of the teres major muscle to the outer border of the first rib where it becomes the subclavian vein.Retrospective Studies: Studies used to test etiologic hypotheses in which inferences about an exposure to putative causal factors are derived from data relating to characteristics of persons under study or to events or experiences in their past. The essential feature is that some of the persons under study have the disease or outcome of interest and their characteristics are compared with those of unaffected persons.Retinal Vein Occlusion: Blockage of the RETINAL VEIN. Those at high risk for this condition include patients with HYPERTENSION; DIABETES MELLITUS; ATHEROSCLEROSIS; and other CARDIOVASCULAR DISEASES.Blood Vessel Prosthesis: Device constructed of either synthetic or biological material that is used for the repair of injured or diseased blood vessels.Magnetic Resonance Angiography: Non-invasive method of vascular imaging and determination of internal anatomy without injection of contrast media or radiation exposure. The technique is used especially in CEREBRAL ANGIOGRAPHY as well as for studies of other vascular structures.Syndrome: A characteristic symptom complex.Time Factors: Elements of limited time intervals, contributing to particular results or situations.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)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.Lumbar Vertebrae: VERTEBRAE in the region of the lower BACK below the THORACIC VERTEBRAE and above the SACRAL VERTEBRAE.Recurrence: The return of a sign, symptom, or disease after a remission.Acute Disease: Disease having a short and relatively severe course.Graft Occlusion, Vascular: Obstruction of flow in biological or prosthetic vascular grafts.Human Umbilical Vein Endothelial Cells: Endothelial cells that line venous vessels of the UMBILICAL CORD.Thrombophlebitis: Inflammation of a vein associated with a blood clot (THROMBUS).Endothelium, Vascular: Single pavement layer of cells which line the luminal surface of the entire vascular system and regulate the transport of macromolecules and blood components.Vascular Grafting: Surgical insertion of BLOOD VESSEL PROSTHESES, or transplanted BLOOD VESSELS, or other biological material to repair injured or diseased blood vessels.Catheter Ablation: Removal of tissue with electrical current delivered via electrodes positioned at the distal end of a catheter. Energy sources are commonly direct current (DC-shock) or alternating current at radiofrequencies (usually 750 kHz). The technique is used most often to ablate the AV junction and/or accessory pathways in order to interrupt AV conduction and produce AV block in the treatment of various tachyarrhythmias.Venous Pressure: The blood pressure in the VEINS. It is usually measured to assess the filling PRESSURE to the HEART VENTRICLE.Venae Cavae: The inferior and superior venae cavae.Sclerotherapy: Treatment of varicose veins, hemorrhoids, gastric and esophageal varices, and peptic ulcer hemorrhage by injection or infusion of chemical agents which cause localized thrombosis and eventual fibrosis and obliteration of the vessels.Venous Valves: Flaps within the VEINS that allow the blood to flow only in one direction. They are usually in the medium size veins that carry blood to the heart against gravity.Liver Circulation: The circulation of BLOOD through the LIVER.Tissue and Organ Harvesting: The procedure of removing TISSUES, organs, or specimens from DONORS for reuse, such as TRANSPLANTATION.Hypertension, Portal: Abnormal increase of resistance to blood flow within the hepatic PORTAL SYSTEM, frequently seen in LIVER CIRRHOSIS and conditions with obstruction of the PORTAL VEIN.Portal System: A system of vessels in which blood, after passing through one capillary bed, is conveyed through a second set of capillaries before it returns to the systemic circulation. It pertains especially to the hepatic portal system.Pulmonary Veno-Occlusive Disease: Pathological process resulting in the fibrous obstruction of the small- and medium-sized PULMONARY VEINS and PULMONARY HYPERTENSION. Veno-occlusion can arise from fibrous proliferation of the VASCULAR INTIMA and VASCULAR MEDIA; THROMBOSIS; or a combination of both.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.Vein of Galen Malformations: Congenital arteriovenous malformation involving the VEIN OF GALEN, a large deep vein at the base of the brain. The rush of arterial blood directly into the vein of Galen, without passing through the CAPILLARIES, can overwhelm the heart and lead to CONGESTIVE HEART FAILURE.Catheterization, Central Venous: Placement of an intravenous CATHETER in the subclavian, jugular, or other central vein.Upper Extremity Deep Vein Thrombosis: DEEP VEIN THROMBOSIS of an upper extremity vein (e.g., AXILLARY VEIN; SUBCLAVIAN VEIN; and JUGULAR VEINS). It is associated with mechanical factors (Upper Extremity Deep Vein Thrombosis, Primary) secondary to other anatomic factors (Upper Extremity Deep Vein Thrombosis, Secondary). Symptoms may include sudden onset of pain, warmth, redness, blueness, and swelling in the arm.Femoral Artery: The main artery of the thigh, a continuation of the external iliac artery.Muscle, Smooth, Vascular: The nonstriated involuntary muscle tissue of blood vessels.Endothelial Cells: Highly specialized EPITHELIAL CELLS that line the HEART; BLOOD VESSELS; and lymph vessels, forming the ENDOTHELIUM. They are polygonal in shape and joined together by TIGHT JUNCTIONS. The tight junctions allow for variable permeability to specific macromolecules that are transported across the endothelial layer.Vena Cava, Superior: The venous trunk which returns blood from the head, neck, upper extremities and chest.Heart Atria: The chambers of the heart, to which the BLOOD returns from the circulation.Regional Blood Flow: The flow of BLOOD through or around an organ or region of the body.Postoperative Complications: Pathologic processes that affect patients after a surgical procedure. They may or may not be related to the disease for which the surgery was done, and they may or may not be direct results of the surgery.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)Hepatic Artery: A branch of the celiac artery that distributes to the stomach, pancreas, duodenum, liver, gallbladder, and greater omentum.Cells, Cultured: Cells propagated in vitro in special media conducive to their growth. Cultured cells are used to study developmental, morphologic, metabolic, physiologic, and genetic processes, among others.Hyperplasia: An increase in the number of cells in a tissue or organ without tumor formation. It differs from HYPERTROPHY, which is an increase in bulk without an increase in the number of cells.Blood Flow Velocity: A value equal to the total volume flow divided by the cross-sectional area of the vascular bed.Sclerosing Solutions: Chemical agents injected into blood vessels and lymphatic sinuses to shrink or cause localized THROMBOSIS; FIBROSIS, and obliteration of the vessels. This treatment is applied in a number of conditions such as VARICOSE VEINS; HEMORRHOIDS; GASTRIC VARICES; ESOPHAGEAL VARICES; PEPTIC ULCER HEMORRHAGE.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.Arteries: The vessels carrying blood away from the heart.Laser Therapy: The use of photothermal effects of LASERS to coagulate, incise, vaporize, resect, dissect, or resurface tissue.Ischemia: A hypoperfusion of the BLOOD through an organ or tissue caused by a PATHOLOGIC CONSTRICTION or obstruction of its BLOOD VESSELS, or an absence of BLOOD CIRCULATION.Ultrasonography, Doppler: Ultrasonography applying the Doppler effect, with frequency-shifted ultrasound reflections produced by moving targets (usually red blood cells) in the bloodstream along the ultrasound axis in direct proportion to the velocity of movement of the targets, to determine both direction and velocity of blood flow. (Stedman, 25th ed)Aneurysm: Pathological outpouching or sac-like dilatation in the wall of any blood vessel (ARTERIES or VEINS) or the heart (HEART ANEURYSM). It indicates a thin and weakened area in the wall which may later rupture. Aneurysms are classified by location, etiology, or other characteristics.Angiography: Radiography of blood vessels after injection of a contrast medium.Budd-Chiari Syndrome: A condition in which the hepatic venous outflow is obstructed anywhere from the small HEPATIC VEINS to the junction of the INFERIOR VENA CAVA and the RIGHT ATRIUM. Usually the blockage is extrahepatic and caused by blood clots (THROMBUS) or fibrous webs. Parenchymal FIBROSIS is uncommon.Popliteal Artery: The continuation of the femoral artery coursing through the popliteal fossa; it divides into the anterior and posterior tibial arteries.Vascular Malformations: A spectrum of congenital, inherited, or acquired abnormalities in BLOOD VESSELS that can adversely affect the normal blood flow in ARTERIES or VEINS. Most are congenital defects such as abnormal communications between blood vessels (fistula), shunting of arterial blood directly into veins bypassing the CAPILLARIES (arteriovenous malformations), formation of large dilated blood blood-filled vessels (cavernous angioma), and swollen capillaries (capillary telangiectases). In rare cases, vascular malformations can result from trauma or diseases.Tunica Intima: The innermost layer of an artery or vein, made up of one layer of endothelial cells and supported by an internal elastic lamina.Phlebitis: Inflammation of a vein, often a vein in the leg. Phlebitis associated with a blood clot is called (THROMBOPHLEBITIS).Reoperation: A repeat operation for the same condition in the same patient due to disease progression or recurrence, or as followup to failed previous surgery.Liver: A large lobed glandular organ in the abdomen of vertebrates that is responsible for detoxification, metabolism, synthesis and storage of various substances.Stockings, Compression: Tight coverings for the foot and leg that are worn to aid circulation in the legs, and prevent the formation of EDEMA and DEEP VEIN THROMBOSIS. PNEUMATIC COMPRESSION STOCKINGS serve a similar purpose especially for bedridden patients, and following surgery.Endoscopy: Procedures of applying ENDOSCOPES for disease diagnosis and treatment. Endoscopy involves passing an optical instrument through a small incision in the skin i.e., percutaneous; or through a natural orifice and along natural body pathways such as the digestive tract; and/or through an incision in the wall of a tubular structure or organ, i.e. transluminal, to examine or perform surgery on the interior parts of the body.Hepatectomy: Excision of all or part of the liver. (Dorland, 28th ed)Cranial Sinuses: Large endothelium-lined venous channels situated between the two layers of DURA MATER, the endosteal and the meningeal layers. They are devoid of valves and are parts of the venous system of dura mater. Major cranial sinuses include a postero-superior group (such as superior sagittal, inferior sagittal, straight, transverse, and occipital) and an antero-inferior group (such as cavernous, petrosal, and basilar plexus).Varicocele: A condition characterized by the dilated tortuous veins of the SPERMATIC CORD with a marked left-sided predominance. Adverse effect on male fertility occurs when varicocele leads to an increased scrotal (and testicular) temperature and reduced testicular volume.Electrophysiologic Techniques, Cardiac: Methods to induce and measure electrical activities at specific sites in the heart to diagnose and treat problems with the heart's electrical system.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.Portography: Examination of the portal circulation by the use of X-ray films after injection of radiopaque material.Mammary Arteries: Arteries originating from the subclavian or axillary arteries and distributing to the anterior thoracic wall, mediastinal structures, diaphragm, pectoral muscles and mammary gland.WingNorepinephrine: 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.Vasoconstriction: The physiological narrowing of BLOOD VESSELS by contraction of the VASCULAR SMOOTH MUSCLE.Catheters, Indwelling: Catheters designed to be left within an organ or passage for an extended period of time.Embolization, Therapeutic: A method of hemostasis utilizing various agents such as Gelfoam, silastic, metal, glass, or plastic pellets, autologous clot, fat, and muscle as emboli. It has been used in the treatment of spinal cord and INTRACRANIAL ARTERIOVENOUS MALFORMATIONS, renal arteriovenous fistulas, gastrointestinal bleeding, epistaxis, hypersplenism, certain highly vascular tumors, traumatic rupture of blood vessels, and control of operative hemorrhage.Transplantation, Autologous: Transplantation of an individual's own tissue from one site to another site.Postphlebitic Syndrome: A condition characterized by a chronically swollen limb, often a leg with stasis dermatitis and ulcerations. This syndrome can appear soon after phlebitis or years later. Postphlebitic syndrome is the result of damaged or incompetent venous valves in the limbs. Distended, tortuous VARICOSE VEINS are usually present. Leg pain may occur after long period of standing.Esophageal and Gastric Varices: Dilated blood vessels in the ESOPHAGUS or GASTRIC FUNDUS that shunt blood from the portal circulation (PORTAL SYSTEM) to the systemic venous circulation. Often they are observed in individuals with portal hypertension (HYPERTENSION, PORTAL).Portasystemic Shunt, Surgical: Surgical venous shunt between the portal and systemic circulation to effect decompression of the portal circulation. It is performed primarily in the treatment of bleeding esophageal varices resulting from portal hypertension. Types of shunt include portacaval, splenorenal, mesocaval, splenocaval, left gastric-caval (coronary-caval), portarenal, umbilicorenal, and umbilicocaval.Liver Transplantation: The transference of a part of or an entire liver from one human or animal to another.Cadaver: A dead body, usually a human body.Spermatic Cord: Either of a pair of tubular structures formed by DUCTUS DEFERENS; ARTERIES; VEINS; LYMPHATIC VESSELS; and nerves. The spermatic cord extends from the deep inguinal ring through the INGUINAL CANAL to the TESTIS in the SCROTUM.Dissection: The separation and isolation of tissues for surgical purposes, or for the analysis or study of their structures.Coronary Sinus: A short vein that collects about two thirds of the venous blood from the MYOCARDIUM and drains into the RIGHT ATRIUM. Coronary sinus, normally located between the LEFT ATRIUM and LEFT VENTRICLE on the posterior surface of the heart, can serve as an anatomical reference for cardiac procedures.Thigh: The portion of the leg in humans and other animals found between the HIP and KNEE.Blood Vessels: Any of the tubular vessels conveying the blood (arteries, arterioles, capillaries, venules, and veins).Vasoconstrictor Agents: Drugs used to cause constriction of the blood vessels.Dose-Response Relationship, Drug: The relationship between the dose of an administered drug and the response of the organism to the drug.