This is a problem with the blood vessels that deliver blood to the heart muscle. If these blood vessels get very small, or if they become blocked, blood cannot flow through them normally. Since less blood is supplied to the heart muscle, the muscle cannot work at normal capacity. The heart muscle can become sick and weak. Heart muscle can even die if blood flow stops. Blocked arteries in the heart are often caused by smoking, high cholesterol, high blood pressure, diabetes, and inherited traits from parents. All of these problems damage the lining of the heart's blood vessels and make them become narrowed or blocked completely.source:wikipedia
