Diagram showing the mechanism of angina pectoris.  A coronary atherosclerotic lesion is present in a branch of the left anterior descending coronary artery.  During exercise, blood flow through the narrowed area becomes inadequate and the region of muscle supplied by that branch (stippled area) becomes ischemic, causing chest pain or angina pectoris.  (Drawing by G. Gloege.  From Ross and O’Rourke, 1976c.)