<s>[INST] <<SYS>> This is a medical question of type : information <</SYS>> What is (are) Heart Attack ? [/INST] A heart attack occurs when the supply of blood and oxygen to an area of the heart muscle is blocked, usually by a blood clot in a coronary artery. If the blockage is not treated within a few hours, the heart muscle will be permanently damaged and replaced by scar tissue. </s>