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What is a heart attack?

When the blood supply to the heart is slowed or stopped because of a blockage, a heart attack occurs. Atherosclerosis, the narrowing of coronary arteries due to plaque buildup, causes more than 90% of heart attacks. A heart attack may also occur when a coronary artery temporarily contracts or goes into a severe spasm, effectively shutting off the flow of blood to the heart. The length of time the blood supply is cut off will determine the amount of damage to the heart.

Read about heart attack warning signs.

Some heart attacks may not affect the heart's functioning, but others may interfere with its ability to pump blood effectively. Sometimes a heart attack may lead to cardiac arrest.

Read about the anatomy of the heart.

Last reviewed March 2011.