Heart
This article is about the internal organ. For other uses, see Heart (disambiguation).
The heart is a muscular organ in humans and other animals, which pumps blood through the blood vesselsof the circulatory system.[1] The blood provides the body with oxygen andnutrients, as well as removing metabolic wastes.[2] The heart is located in the middle compartment of themediastinum in the chest.[3]
In humans, other mammals and birds the heart is divided into four chambers: upper left and right atria; and lower left and right ventricles.[4][5] Commonly the right atrium and ventricle are referred together as the right heart and their left counterparts as the left heart.[6] Fish in contrast have two chambers, an atrium and a ventricle, while reptiles have three chambers.[5] Blood normally flows one way through the heart due to heart valves, which prevent backflow.[3] The heart is enclosed in a protective sac, thepericardium, which also contains a small amount of fluid. The wall of the heart is made up of three layers:epicardium; myocardium; andendocardium.[7]
The heart pumps blood through both circulatory systems. Blood low in oxygen from the systemic circulationenters the right atrium from the superiorand inferior vena cavae and then passes to the right ventricle. From here it is pumped through the pulmonary circulation, to the lungs where it receives oxygen and gives off carbon dioxide. Oxygenated blood then returns to the left atrium, passes through the left ventricle and is pumped out through the aorta to the systemic circulation−where the oxygen is used andmetabolized to carbon dioxide.[2]Normally with each heartbeat, the right ventricle pumps the same amount of blood into the lungs as the left ventricle pumps out into the body. Veinstransport blood to the heart, whilearteries transport blood away from the heart. Veins normally have lowerpressures than arteries.[2][3] The heart contracts at a rate of roughly 72 beats per minute at rest.[2] Exercisetemporarily increases this rate, but lowers resting heart rate in the long term, and is good for heart health.[8]
Cardiovascular disease (CVD) was the most common cause of death globally in 2008, accounting for 30% of cases.[9][10] Of these deaths more than three quarters were due to coronary artery disease and stroke.[9] Risk factors include: smoking, being overweight, not enough exercise, high cholesterol, high blood pressure, and poorly controlleddiabetes among others.[11] Diagnosis of CVD is often done by listening to theheart-sounds with a stethoscope, ECGor by ultrasound.[3] Diseases of the heart are primarily treated bycardiologists, although many specialties of medicine may be involved.[10]
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