Heart Attack or Acute Myocardial Infarction (or MI) occurs when blood flow to part of the heart is blocked. The blockage is usually caused by either a blood clot, or a plaque (sounds like plak) in a coronary artery. The coronary arteries supply blood and oxygen to the heart muscle. Plaques are collections of fatty and hardened or calcified materials in the wall of an artery associated with a condition called arteriosclerosis or atherosclerosis. When the blood and oxygen supply to the heart is restricted too long without treatment, the result is damage or death (infraction) of heart muscle (myocardium). That’s why the term myocardial infraction is also used for a heart attack.