Hi,
A very informative article.

A heart attack is caused by lack of oxygen-rich blood flow to the heart muscle. Blood flow is usually blocked by a blood clot in one or more of the coronary arteries around the heart. Cholesterol buildup can occur in these blood vessels in the form of plaque. This narrows the artery and can restrict the amount of blood that can flow through it. If the artery becomes too narrow, it cannot supply enough blood to the heart muscle when it becomes stressed. Just like arm muscles that begin to hurt if you lift too much, or legs that ache when you run too fast; the heart muscle will ache if it doesn't get adequate blood supply. This ache is called angina. If the plaque ruptures, a small blood clot can form within the blood vessel and acutely block the blood flow. When that part of the heart loses its blood supply completely, the muscle dies. This is called a heart attack.