What is a heart attack?

A heart attack occurs when the blood supply to part of the heart muscle itself is severely reduced or stopped. The reduction or stoppage happens when one or more of the coronary arteries supplying blood to the heart muscle is blocked. This is usually caused by the build up of plaque, a process called atherosclerosis. The plaque can eventually burst, tear or rupture, creating a "snag" where a blood clot forms and blocks the artery. This leads to a heart attack.

If the blood supply is cut off for more than a few minutes, muscle cells suffer permanent injury and die. This can kill or disable someone, depending on how much heart muscle is damaged.

Sometimes a coronary artery temporarily contracts or goes into spasm. When this happens the artery narrows and blood flow to part of the heart muscle decreases or stops. We're not sure what causes a spasm. A spasm can occur in normal-appearing blood vessels as well as in vessels partly blocked by atherosclerosis. A severe spasm can cause a heart attack.

The medical term for heart attack is myocardial infarction. A heart attack is also sometimes called a coronary thrombosis or coronary occlusion.

(http://www.americanheart.org/presenter.jhtml?identifier=4578)