Over the time the arteries carrying blood and oxygen get choked with plaques, a formation of cholesterol. A heart attack occurs when this plaque ruptures and a blood clot forms at the spot.

If the blood clot is large enough it restricts the supply of blood to that part of the heart muscle. The narrowing of arteries is called the coronary heart disease and it is the major cause of heart attack.An exceptional cause of heart attack is the spasm of the coronary artery which blocks the supply of blood to heart muscle. Drugs like cocaine can induce such a spasm.