In the early years of the clinical recognition of coronary occlusion, substernal or epigastric pain of at least several hours' duration was considered to be a characteristic feature. Subsequent observations have shown not only that this type of pain may be closely simulated by other conditions, such as acute surgical disorders of the abdomen, pulmonary embolism, dissecting aneurysm of the aorta, interstitial emphysema and pneumothorax, but also that painless occlusion of the coronary artery may occur in a certain number of cases, with dyspnea replacing pain most frequently as the presenting symptom. The clinical picture here is that of failure of the left ventricle, followed by congestive heart failure. In a still smaller percentage of cases the severe initial anginal pain may be replaced by symptoms suggesting a cerebral vascular lesion, such as sudden weakness, dizziness, syncope and unconsciousness, or by gastrointestinal features, such as nausea, vomiting, distention, obstipation and