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The heart has four chambers: The left ventricle (the strongest chamber) pumps oxygen-rich blood to the rest of the body. This is an emergency situation as it can precede a heart attack, serious abnormal heart rhythm, or cardiac arrest.
Table of contents
In fishes the heart is a folded tube, with three or four enlarged areas that correspond to the chambers in the mammalian heart.source site
Picture of the Heart
In animals with lungs—amphibians, reptiles, birds, and mammals—the heart shows various stages of evolution from a single to a double pump that circulates blood 1 to the lungs and 2 to the body as a whole. In vertebrates blood and lymph the circulating fluids have an essential role in maintaining homeostasis the constancy of the internal environment by distributing substances to parts of the body when required and by removing others from areas in which their accumulation would be harmful.
In humans and other mammals and in birds , the heart is a four-chambered double pump that is the centre of the circulatory system. In humans it is situated between the two lungs and slightly to the left of centre, behind the breastbone; it rests on the diaphragm , the muscular partition between the chest and the abdominal cavity.
The heart consists of several layers of a tough muscular wall, the myocardium. A thin layer of tissue , the pericardium , covers the outside, and another layer, the endocardium , lines the inside. The heart cavity is divided down the middle into a right and a left heart, which in turn are subdivided into two chambers. The upper chamber is called an atrium or auricle , and the lower chamber is called a ventricle. The two atria act as receiving chambers for blood entering the heart; the more muscular ventricles pump the blood out of the heart.
The heart, although a single organ, can be considered as two pumps that propel blood through two different circuits. The right atrium receives venous blood from the head , chest, and arms via the large vein called the superior vena cava and receives blood from the abdomen , pelvic region, and legs via the inferior vena cava. Blood then passes through the tricuspid valve to the right ventricle, which propels it through the pulmonary artery to the lungs. In the lungs venous blood comes in contact with inhaled air, picks up oxygen , and loses carbon dioxide.
Oxygenated blood is returned to the left atrium through the pulmonary veins. Valves in the heart allow blood to flow in one direction only and help maintain the pressure required to pump the blood. The low-pressure circuit from the heart right atrium and right ventricle , through the lungs, and back to the heart left atrium constitutes the pulmonary circulation.
Passage of blood through the left atrium, bicuspid valve, left ventricle, aorta , tissues of the body, and back to the right atrium constitutes the systemic circulation. Blood pressure is greatest in the left ventricle and in the aorta and its arterial branches. Pressure is reduced in the capillaries vessels of minute diameter and is reduced further in the veins returning blood to the right atrium.
The pumping of the heart, or the heartbeat , is caused by alternating contractions and relaxations of the myocardium. These contractions are stimulated by electrical impulses from a natural pacemaker, the sinoatrial , or S-A, node located in the muscle of the right atrium. An impulse from the S-A node causes the two atria to contract, forcing blood into the ventricles.
Contraction of the ventricles is controlled by impulses from the atrioventricular , or A-V, node located at the junction of the two atria. Following contraction, the ventricles relax, and pressure within them falls. Blood again flows into the atria, and an impulse from the S-A starts the cycle over again. This process is called the cardiac cycle. The period of relaxation is called diastole. A coagulation screen is often required to ensure that the right level of anticoagulation is given.
Fasting lipids and fasting blood glucose or an HbA1c level are often ordered to evaluate a person's cholesterol and diabetes status, respectively. Using surface electrodes on the body, it is possible to record the electrical activity of the heart. An ECG is a bedside test and involves the placement of ten leads on the body.
This produces a "12 lead" ECG three extra leads are calculated mathematically, and one lead is a ground. There are five prominent features on the ECG: A downward deflection on the ECG implies cells are becoming more positive in charge "depolarising" in the direction of that lead, whereas an upward inflection implies cells are becoming more negative "repolarising" in the direction of the lead. This depends on the position of the lead, so if a wave of depolarising moved from left to right, a lead on the left would show a negative deflection, and a lead on the right would show a positive deflection.
The ECG is a useful tool in detecting rhythm disturbances and in detecting insufficient blood supply to the heart. Testing when exercising can be used to provoke an abnormality, or an ECG can be worn for a longer period such as a hour Holter monitor if a suspected rhythm abnormality is not present at the time of assessment. Several imaging methods can be used to assess the anatomy and function of the heart, including ultrasound echocardiography , angiography , CT scans , MRI and PET. An echocardiogram is an ultrasound of the heart used to measure the heart's function, assess for valve disease, and look for any abnormalities.
Echocardiography can be conducted by a probe on the chest "transthoracic" or by a probe in the esophagus "transoesophageal". A typical echocardiography report will include information about the width of the valves noting any stenosis , whether there is any backflow of blood regurgitation and information about the blood volumes at the end of systole and diastole, including an ejection fraction , which describes how much blood is ejected from the left and right ventricles after systole.
Ejection fraction can then be obtained by dividing the volume ejected by the heart stroke volume by the volume of the filled heart end-diastolic volume. This cardiac stress test involves either direct exercise, or where this is not possible, injection of a drug such as dobutamine.
CT scans, chest X-rays and other forms of imaging can help evaluate the heart's size, evaluate for signs of pulmonary oedema , and indicate whether there is fluid around the heart. They are also useful for evaluating the aorta, the major blood vessel which leaves the heart. Diseases affecting the heart can be treated by a variety of methods including lifestyle modification, drug treatment, and surgery.
Narrowings of the coronary arteries ischaemic heart disease are treated to relieve symptoms of chest pain caused by a partially narrowed artery angina pectoris , to minimise heart muscle damage when an artery is completely occluded myocardial infarction , or to prevent a myocardial infarction from occurring. Medications to improve angina symptoms include nitroglycerin , beta blockers , and calcium channel blockers, while preventative treatments include antiplatelets such as aspirin and statins , lifestyle measures such as stopping smoking and weight loss, and treatment of risk factors such as high blood pressure and diabetes.
In addition to using medications, narrowed heart arteries can be treated by expanding the narrowings or redirecting the flow of blood to bypass an obstruction.
This may be performed using a percutaneous coronary intervention , during which narrowings can be expanded by passing small balloon-tipped wires into the coronary arteries, inflating the balloon to expand the narrowing, and sometimes leaving behind a metal scaffold known as a stent to keep the artery open.
If the narrowings in coronary arteries are unsuitable for treatment with a percutaneous coronary intervention, open surgery may be required. A coronary artery bypass graft can be performed, whereby a blood vessel from another part of the body the saphenous vein , radial artery , or internal mammary artery is used to redirect blood from a point before the narrowing typically the aorta to a point beyond the obstruction.
Diseased heart valves that have become abnormally narrow or abnormally leaky may require surgery. This is traditionally performed as an open surgical procedure to replace the damaged heart valve with a tissue or metallic prosthetic valve. In some circumstances, the tricuspid or mitral valves can be repaired surgically , avoiding the need for a valve replacement. Heart valves can also be treated percutaneously, using techniques that share many similarities with percutaneous coronary intervention.
Transcatheter aortic valve replacement is increasingly used for patients consider very high risk for open valve replacement. Abnormal heart rhythms arrhythmias can be treated using antiarrhythmic drugs. These may work by manipulating the flow of electrolytes across the cell membrane such as calcium channel blockers , sodium channel blockers , amiodarone , or digoxin , or modify the autonomic nervous system's effect on the heart beta blockers and atropine. In some arrhythmias such as atrial fibrillation which increase the risk of stroke, this risk can be reduced using anticoagulants such as warfarin or novel oral anticoagualants.
If medications fail to control an arrhythmia, another treatment option may be catheter ablation. In these procedures, wires are passed from a vein or artery in the leg to the heart to find the abnormal area of tissue that is causing the arrhythmia. The abnormal tissue can be intentionally damaged, or ablated, by heating or freezing to prevent further heart rhythm disturbances. Whilst the majority of arrhythmias can be treated using minimally invasive catheter techniques, some arrhythmias particularly atrial fibrillation can also be treated using open or thoracoscopic surgery, either at the time of other cardiac surgery or as a standalone procedure.
A cardioversion , whereby an electric shock is used to stun the heart out of an abnormal rhythm, may also be used. Cardiac devices in the form of pacemakers or implantable defibrillators may also be required to treat arrhythmias. Pacemakers, comprising a small battery powered generator implanted under the skin and one or more leads that extend to the heart, are most commonly used to treat abnormally slow heart rhythms. These devices monitor the heart, and if dangerous heart racing is detected can automatically deliver a shock to restore the heart to a normal rhythm.
Implantable defibrillators are most commonly used in patients with heart failure , cardiomyopathies , or inherited arrhythmia syndromes. As well as addressing the underlying cause for a patient's heart failure most commonly ischaemic heart disease or hypertension , the mainstay of heart failure treatment is with medication. These include drugs to prevent fluid from accumulating in the lungs by increasing the amount of urine a patient produces diuretics , and drugs that attempt to preserve the pumping function of the heart beta blockers , ACE inhibitors and mineralocorticoid receptor antagonists.
In some patients with heart failure, a specialised pacemaker known as cardiac resynchronisation therapy can be used to improve the heart's pumping efficiency. In very severe cases of heart failure, a small pump called a ventricular assist device may be implanted which supplements the heart's own pumping ability. In the most severe cases, a cardiac transplant may be considered.
Humans have known about the heart since ancient times, although its precise function and anatomy were not clearly understood. He also discovered the heart valves. The Greek physician Galen 2nd century CE knew blood vessels carried blood and identified venous dark red and arterial brighter and thinner blood, each with distinct and separate functions.
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These ideas went unchallenged for almost a thousand years. The earliest descriptions of the coronary and pulmonary circulation systems can be found in the Commentary on Anatomy in Avicenna's Canon , published in by Ibn al-Nafis. In Europe, the teachings of Galen continued to dominate the academic community and his doctrines were adopted as the official canon of the Church.
Andreas Vesalius questioned some of Galen's beliefs of the heart in De humani corporis fabrica , but his magnum opus was interpreted as a challenge to the authorities and he was subjected to a number of attacks. A breakthrough in understanding the flow of blood through the heart and body came with the publication of De Motu Cordis by the English physician William Harvey. Harvey's book completely describes the systemic circulation and the mechanical force of the heart, leading to an overhaul of the Galenic doctrines.
Ernest Starling — was an important English physiologist who also studied the heart. Although they worked largely independently, their combined efforts and similar conclusions have been recognized in the name " Frank—Starling mechanism ". Tawara's discovery of the atrioventricular node prompted Arthur Keith and Martin Flack to look for similar structures in the heart, leading to their discovery of the sinoatrial node several months later.
These structures form the anatomical basis of the electrocardiogram , whose inventor, Willem Einthoven , was awarded the Nobel Prize in Medicine or Physiology in This marked an important milestone in cardiac surgery , capturing the attention of both the medical profession and the world at large. However, long-term survival rates of patients were initially very low. Louis Washkansky , the first recipient of a donated heart, died 18 days after the operation while other patients did not survive for more than a few weeks.
As of March , more than 55, heart transplantations have been performed worldwide. By the middle of the 20th century, heart disease had surpassed infectious disease as the leading cause of death in the United States, and it is currently the leading cause of deaths worldwide.
Since , the ongoing Framingham Heart Study has shed light on the effects of various influences on the heart, including diet, exercise, and common medications such as aspirin. As one of the vital organs, the heart was long identified as the center of the entire body, the seat of life, or emotion, or reason, will, intellect, purpose or the mind. In the Hebrew Bible , the word for heart, lev , is used in these meanings, as the seat of emotion, the mind, and referring to the anatomical organ.
It is also connected in function and symbolism to the stomach. An important part of the concept of the soul in Ancient Egyptian religion was thought to be the heart, or ib. The ib or metaphysical heart was believed to be formed from one drop of blood from the child's mother's heart, taken at conception. This is evidenced by Egyptian expressions which incorporate the word ib , such as Awi-ib for "happy" literally, "long of heart" , Xak-ib for "estranged" literally, "truncated of heart".
It was conceived as surviving death in the nether world, where it gave evidence for, or against, its possessor. It was thought that the heart was examined by Anubis and a variety of deities during the Weighing of the Heart ceremony. If the heart weighed more than the feather of Maat , which symbolized the ideal standard of behavior. If the scales balanced, it meant the heart's possessor had lived a just life and could enter the afterlife; if the heart was heavier, it would be devoured by the monster Ammit.
In Sanskrit, it may mean both the anatomical object and "mind" or "soul", representing the seat of emotion. Hrd may be a cognate of the word for heart in Greek, Latin, and English. Many classical philosophers and scientists, including Aristotle , considered the heart the seat of thought, reason , or emotion, often disregarding the brain as contributing to those functions.
The heart also played a role in the Aztec system of belief. The most common form of human sacrifice practiced by the Aztecs was heart-extraction. The Aztec believed that the heart tona was both the seat of the individual and a fragment of the Sun's heat istli. To this day, the Nahua consider the Sun to be a heart-soul tona-tiuh: In Catholicism , there has been a long tradition of veneration of the heart, stemming from worship of the wounds of Jesus Christ which gained prominence from the mid sixteenth century.
The expression of a broken heart is a cross-cultural reference to grief for a lost one or to unfulfilled romantic love. The notion of " Cupid 's arrows" is ancient, due to Ovid , but while Ovid describes Cupid as wounding his victims with his arrows, it is not made explicit that it is the heart that is wounded. The familiar iconography of Cupid shooting little heart symbols is a Renaissance theme that became tied to Valentine's day. Animal hearts are widely consumed as food. As they are almost entirely muscle, they are high in protein.
They are often included in dishes with other offal , for example in the pan-Ottoman kokoretsi. Chicken hearts are considered to be giblets , and are often grilled on skewers: In Egyptian cuisine , they can be used, finely chopped, as part of stuffing for chicken. The hearts of beef, pork, and mutton can generally be interchanged in recipes.
As heart is a hard-working muscle, it makes for "firm and rather dry" meat,  so is generally slow-cooked. Another way of dealing with toughness is to julienne the meat, as in Chinese stir-fried heart. Beef heart may be grilled or braised. An Australian recipe for "mock goose" is actually braised stuffed beef heart. Pig heart is stewed, poached, braised,  or made into sausage. The Balinese oret is a sort of blood sausage made with pig heart and blood. The SA node is found in all amniotes but not in more primitive vertebrates. In these animals, the muscles of the heart are relatively continuous, and the sinus venosus coordinates the beat, which passes in a wave through the remaining chambers.
Indeed, since the sinus venosus is incorporated into the right atrium in amniotes, it is likely homologous with the SA node. In teleosts, with their vestigial sinus venosus, the main centre of coordination is, instead, in the atrium. The rate of heartbeat varies enormously between different species, ranging from around 20 beats per minute in codfish to around in hummingbirds  and up to bpm in the ruby-throated hummingbird.
Adult amphibians and most reptiles have a double circulatory system , meaning a circulatory system divided into arterial and venous parts. However, the heart itself is not completely separated into two sides. Instead, it is separated into three chambers — two atria and one ventricle. Blood returning from both the systemic circulation and the lungs is returned, and blood is pumped simultaneously into the systemic circulation and the lungs.
The double system allows blood to circulate to and from lungs which deliver oxygenated blood directly to the heart. In reptiles, the heart is usually situated around the middle of the thorax, and in snakes, usually between the junction of the upper first and second third.
There is a heart with three chambers: The ventricle is incompletely separated into two halves by a wall septum , with a considerable gap near the pulmonary artery and aortic openings. In most reptilian species, there appears to be little, if any, mixing between the bloodstreams, so the aorta receives, essentially, only oxygenated blood. In the heart of lungfish , the septum extends part-way into the ventricle.
This allows for some degree of separation between the de-oxygenated bloodstream destined for the lungs and the oxygenated stream that is delivered to the rest of the body. The absence of such a division in living amphibian species may be partly due to the amount of respiration that occurs through the skin; thus, the blood returned to the heart through the venae cavae is already partially oxygenated.
As a result, there may be less need for a finer division between the two bloodstreams than in lungfish or other tetrapods. Nonetheless, in at least some species of amphibian, the spongy nature of the ventricle does seem to maintain more of a separation between the bloodstreams. Also, the original valves of the conus arteriosus have been replaced by a spiral valve that divides it into two parallel parts, thereby helping to keep the two bloodstreams separate. Archosaurs crocodilians and birds and mammals show complete separation of the heart into two pumps for a total of four heart chambers ; it is thought that the four-chambered heart of archosaurs evolved independently from that of mammals.
In crocodilians, there is a small opening, the foramen of Panizza , at the base of the arterial trunks and there is some degree of mixing between the blood in each side of the heart, during a dive underwater;   thus, only in birds and mammals are the two streams of blood — those to the pulmonary and systemic circulations — permanently kept entirely separate by a physical barrier.
Fish have what is often described as a two-chambered heart,  consisting of one atrium to receive blood and one ventricle to pump it. The atrium and ventricle are sometimes considered "true chambers", while the others are considered "accessory chambers". Primitive fish have a four-chambered heart, but the chambers are arranged sequentially so that this primitive heart is quite unlike the four-chambered hearts of mammals and birds.
The first chamber is the sinus venosus , which collects deoxygenated blood from the body through the hepatic and cardinal veins. From here, blood flows into the atrium and then to the powerful muscular ventricle where the main pumping action will take place. The fourth and final chamber is the conus arteriosus , which contains several valves and sends blood to the ventral aorta. The ventral aorta delivers blood to the gills where it is oxygenated and flows, through the dorsal aorta , into the rest of the body. In tetrapods , the ventral aorta has divided in two; one half forms the ascending aorta , while the other forms the pulmonary artery.
In the adult fish, the four chambers are not arranged in a straight row but instead form an S-shape, with the latter two chambers lying above the former two. This relatively simpler pattern is found in cartilaginous fish and in the ray-finned fish. In teleosts , the conus arteriosus is very small and can more accurately be described as part of the aorta rather than of the heart proper. The conus arteriosus is not present in any amniotes , presumably having been absorbed into the ventricles over the course of evolution. Similarly, while the sinus venosus is present as a vestigial structure in some reptiles and birds, it is otherwise absorbed into the right atrium and is no longer distinguishable.
Arthropods and most mollusks have an open circulatory system. In this system, deoxygenated blood collects around the heart in cavities sinuses. This blood slowly permeates the heart through many small one-way channels. The heart then pumps the blood into the hemocoel , a cavity between the organs. The heart in arthropods is typically a muscular tube that runs the length of the body, under the back and from the base of the head. Instead of blood the circulatory fluid is haemolymph which carries the most commonly used respiratory pigment , copper-based haemocyanin as the oxygen transporter; iron-based haemoglobin is used by only a few arthropods.
In some other invertebrates such as earthworms , the circulatory system is not used to transport oxygen and so is much reduced, having no veins or arteries and consisting of two connected tubes. Oxygen travels by diffusion and there are five small muscular vessels that connect these vessels that contract at the front of the animals that can be thought of as "hearts". Squids and other cephalopods have two "gill hearts" also known as branchial hearts , and one "systemic heart".
The brachial hearts have two atria and one ventricle each, and pump to the gills , whereas the systemic heart pumps to the body. This article incorporates text from the CC-BY book: From Wikipedia, the free encyclopedia. This article is about the internal organ. For other uses, see Heart disambiguation. For the comics character, see Cardiac comics. Normal heart sounds as heard with a stethoscope. With the atria and major vessels removed, all four valves are clearly visible. The heart, showing valves, arteries and veins. The white arrows show the normal direction of blood flow.
Heart development and Human embryogenesis. Cardiac cycle , Systole , and Diastole. Electrical conduction system of the heart and Heart rate. The stethoscope is used for auscultation of the heart, and is one of the most iconic symbols for medicine. A number of diseases can be detected primarily by listening for heart murmurs. Atherosclerosis is a condition affecting the circulatory system. If the coronary arteries are affected, angina pectoris may result or at worse a heart attack.
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Cardiac examination and Heart sounds. Coronary artery disease , Coronary artery bypass surgery , and Coronary stent. Heart arrhythmia , Radiofrequency ablation , and Artificial cardiac pacemaker. The seal script glyph for "heart" Middle Chinese sim. Blood flow through the fish heart: The pressure difference between the blood in the atria and the ventricles does this. Taber's cyclopedic medical dictionary.
Today and Tomorrow With Physiology. Archived from the original on 2 May California Subject Examinations for Teachers 3rd ed. Archived from the original on 4 May Retrieved 11 August Archived from the original on 19 September Retrieved 20 September Harrison's Principles of Internal Medicine 18 ed. Surface Markings of the Thorax". Archived from the original on 20 November Retrieved 18 October Dorland's Illustrated Medical Dictionary 32nd ed. Archived from the original on 29 July Retrieved 14 August They let blood flow from the atria to the ventricles.
The other two are called the aortic say: PUL-muh-ner-ee valve , and they're in charge of controlling the flow as the blood leaves the heart. These valves all work to keep the blood flowing forward. They open up to let the blood move ahead, then they close quickly to keep the blood from flowing backward. You probably guessed that the blood just doesn't slosh around your body once it leaves the heart. It moves through many tubes called arteries and veins , which together are called blood vessels.
These blood vessels are attached to the heart. The blood vessels that carry blood away from the heart are called arteries. The ones that carry blood back to the heart are called veins. The movement of the blood through the heart and around the body is called circulation say: Your body needs this steady supply of blood to keep it working right. Blood delivers oxygen to all the body's cells. To stay alive, a person needs healthy, living cells.
Without oxygen, these cells would die. If that oxygen-rich blood doesn't circulate as it should, a person could die. The left side of your heart sends that oxygen-rich blood out to the body. The body takes the oxygen out of the blood and uses it in your body's cells. When the cells use the oxygen, they make carbon dioxide and other stuff that gets carried away by the blood. It's like the blood delivers lunch to the cells and then has to pick up the trash! The returning blood enters the right side of the heart. The right ventricle pumps the blood to the lungs for a little freshening up.
In the lungs, carbon dioxide is removed from the blood and sent out of the body when we exhale. An inhale, of course, and a fresh breath of oxygen that can enter the blood to start the process again. And remember, it all happens in about a minute! When you go for a checkup, your doctor uses a stethoscope to listen carefully to your heart. A healthy heart makes a lub-dub sound with each beat.
This sound comes from the valves shutting on the blood inside the heart.
Your Heart & Circulatory System
The first sound the lub happens when the mitral and tricuspid valves close. The next sound the dub happens when the aortic and pulmonary valves close after the blood has been squeezed out of the heart. Next time you go to the doctor, ask if you can listen to the lub-dub, too.