heart

HEART The human heart is a specialized, four-chambered muscle that maintains BLOOD flow in the CIRCULATORY SYSTEM. Located in the thorax, it lies left of the body's midline, above and in contact with the diaphragm. It is situated immediately behind the breastbone, or sternum, and between the lungs, with its apex tilted to the body cavity's left side. In most people the apex can be felt during each heart contraction. At rest, the heart pumps …

…chest wall. The electrocardiogram (cardiogram, ECG) that is obtained in this way furnishes information about the rhythm of the heart, the conduction of the stimulus, and the condition of the heart muscle. Other methods that have been devised to examine the heart are the mechanical recording of the heartbeat, echocendiography and radioisotopes, X-ray analysis of the heart's form and movements, and X-ray contrast studies of the blood flow through the heart and the coronary vessels.