The coronary arteries in patients who die of an acute myocardial infarction may be anatomically normal or they may have a combination of lesions. They may show only marked atherosclerosis, with or without special features such as intramural hemorrhage or plaque rupture. There may also be thrombotic occlusion of the lumen of the artery. Whether this thrombotic process usually occurs before the myocardial infarction or whether it sometimes follows and results from the infarct is not known.