This study is designed to examine the blood flow, the nutrition, and the beating function of the heart under different conditions. Patients with narrowed coronary arteries my have restricted blood flow to the heart. The lowered blood supply to the heart muscle may not cause symptoms immediately. However, as the heart pumps faster and harder the blood supply demand is increased. If blood flow is unable supply enough oxygen and nutrition to heart muscle patients can experience symptoms of chest pain and shortness of breath. Even after the heart slows down and demand for oxygen and nutrition is reduced, patients can still experience pain and abnormal heart function.