Myocardial infarction (MI) occurs when myocardial tissue is abruptly and severely deprive of oxygen. When blood flow is quickly reduced by 80% to 90%, ischemia develops. Ischemia can lead to injury and necrosis of myocardial tissue of blood flow is not restored. Most MIs are the result of atherosclerosis of a coronary artery, rupture of the plaque, subsequent thrombosis, and occlusion (blockage) of bold flow. Other factors may be involved, however, such as coronary artery spasm, platelet aggregation, and emboli from mural thrombi (thrombi lining the walls of the cardiac chambers).