Heart

Heart, muscular organ whose purpose is to pump blood through the body. The human heart is about the size of the closed fist, shaped like a blunt cone and is located in the chest cavity, slightly left of center. The heart is divided into right and left halves by a muscular partition. Each half is subdivided into two cavities, the upper (atrium) and the lower (ventricle). Blood from the veins of the body flows to the right atrium. From there it goes to the right ventricle, which pumps it to the lungs. From the lungs, the blood, now rich in oxygen, is carried back to the left atrium. It then flows into the left ventricle, from where it is pumped throughout the body. A series of valves between the right and left atria and ventricles and at the entrances to the main blood vessels prevent blood from backing up as it circulates. Diseases of the heart and blood vessels, whiche cause about half of all deaths in the United States, are called cardiovascular diseases. Three major kinds of heart disease are hypertension, arteriosclerosis, and rheumatic fever.

See also: Circulatory system.