Over time, plaque can build up along the course of an artery and narrow the channel through which blood flows. Plaque is made up of cholesterol buildup and eventually may calcify or harden, with calcium deposits. 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 ache or hurt when heavy things are lifted, or legs that ache when you run too fast; the heart muscle will ache if it doesn't get adequate blood supply. This ache or pain is called angina. It is important to know that angina can manifest in many different ways and does not always need to be experienced as chest pain.
If the plaque ruptures, a small blood clot can form within the blood vessel, acting like a dam and acutely blocking the blood flow beyond the clot. When that part of the heart loses its blood supply completely, the muscle dies. This is called a heart attack, or an MI - a myocardial infarction (myo=muscle +cardial=heart; infarction=death due to lack of oxygen).
