• Patients with the diagnosis of acute myocardial infarction can be classified as good or poor risks at the time of the first examination. Those who have never had previous infarctions, who do not have intractable pain, extreme or persistent shock, significant cardiac enlargement, gallop rhythm, congestive heart failure, auricular fibrillation or flutter, or ventricular tachycardia or intraventricular block, and who do not have diabetic acidosis or other states predisposing to thrombosis are classified as good risks. Data previously reported are here supplemented by data from 511 good-risk patients who did not receive anticoagulant therapy and were closely watched for thromboembolic complications. The latter occurred in only 3.7% of the cases and all were of a mild nature. There were 18 deaths. Analysis of the causes of death did not yield evidence that anticoagulant therapy would have reduced the mortality to a significant degree. The mortality of 3.5% for the good-risk patients was in marked contrast to the mortality of 60% previously found for poor-risk patients. The authors believe that anticoagulant therapy, which has certain hazards, is neither necessary nor desirable for patients who have been classified as good risks by the above criteria.