Infarction (medically called MI or Coronary Thrombosis) is the consequence of the complete obstruction of Artery that supply blood to a part of the heart muscles. This occurs due to a 100% blockages in any of the coronary arteries or their branches. The heart muscles are completely deprived of their blood and oxygen supply which leads to the death. The severity of the heart attack would depend on how much area of the heart muscle is actually involved. It is mild, if only 5 to 10 % area is involved and most of the patients survive. But if the dead area is more than 30 to 40 % of the heart muscles, the attack is considered severe, and if not managed properly and immediately, can even lead to death.