A questionnaire method was developed for the study of 2,600 cases of proved acute coronary occlusion. The data included the hour, the day, and the type of effort or the mode of rest at the onset of the episode. The results did not show that occupation, exertion, or state of inactivity played any part in precipitating the occlusion. There was no evidence that one attack of acute coronary occlusion predisposed to a second attack except indirectly because of the underlying atherosclerosis. The author does not believe that coronary occlusion has become epidemic or that it is caused by modern stress and strain; he believes that its apparent incidence has increased because of the increased age of the population, improved diagnostic skill of physicians, and changes in the classification of heart diseases.