A heart attack (also known as a myocardial infarction) occurs when the blood flow to part of the heart is interrupted. Blockage of the coronary artery deprives the heart muscles of blood and oxygen, causing injury to some of the heart muscles. This injury causes severe chest pain and chest pressure sensation. If the flow of the blood is not restored within 20 to 40 minutes, irreversible death of the heart muscle will begin to occur. The muscles continue to die for six to eight hours at which the heart attack is complete.