Most heart attacks are caused by a blood clot that blocks one of the coronary arteries (the blood vessels that bring blood and oxygen to the heart muscle). When blood cannot reach part of your heart, that area starves for oxygen. If the blockage continues long enough, cells in the affected area die.

Coronary artery disease (CAD) is the most common underlying cause of a heart attack. CAD is the hardening and narrowing of the coronary arteries by the buildup of plaque in the inside walls (see Atherosclerosis). Over time, plaque buildup in the coronary arteries can:

• Narrow the arteries so that less blood flows to the heart muscle
• Block completely the arteries and the flow of blood
• Cause blood clots to form and block the arteries

A less common cause of heart attacks is a severe spasm (tightening) of the coronary artery that cuts off blood flow to the heart. These spasms can occur in persons with or without CAD. Artery spasm can sometimes be caused by:

• Taking certain drugs, such as cocaine
• Emotional stress
• Exposure to cold
• Cigarette smoking