Heart attacks result from heart disease - blood vessel disease in the heart. Coronary artery disease (C.A.D.) and ischemic heart disease are other names for coronary heart disease.

The medical term for heart attack is myocardial infarction. A heart attack occurs when the blood supply to part of the heart muscle itself - the myocardium - is severely reduced or stopped. This occurs when one of the arteries that supply blood to the heart muscle (coronary arteries) is blocked by an obstruction. The blockage is usually from the buildup of plaque (deposits of fat-like substances) due to atherosclerosis .

A heart attack is often caused by a blood clot forming in a coronary artery. This often results from reaction to rupture or tearing of a plaque that has formed. Such an event is sometimes called a coronary thrombosis or coronary occlusion. A myocardial infarction is the damaging or death of an area of the heart muscle resulting from a reduced blood supply to that area.

If the blood supply is cut off severely or for a long time, muscle cells suffer irreversible injury and die. Disability or death can result, 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 even stops. What causes a spasm is unclear. But it can occur in normal-appearing blood vessels as well as vessels partly blocked by atherosclerosis. If a spasm is severe, a heart attack may result.