A heart attack (also known as a myocardial infarction) is the death of heart muscle from the sudden blockage of a coronary artery by a blood clot.
Coronary arteries are blood vessels that supply the heart muscle with blood and oxygen. Blockage of a coronary artery deprives the heart muscle of blood and oxygen, causing injury to the heart muscle.
Injury to the heart muscle causes chest pain and pressure.
If blood flow is not restored within 20 to 40 minutes, irreversible death of the heart muscle will begin to occur. Muscle continues to die for 6-8 hours at which time the heart attack usually is "complete." The dead heart muscle is replaced by scar tissue.