The authors studied data on heart disease obtained between Jan. 1 and Dec. 31, 1957, from an area containing an estimated population of 100,000. This area was taken as typical, geographically and economically, of the situation usually dealt with by the general physician. There were 40 cases of angina pectoris, 45 of definite or probable coronary insufficiency, 157 of definite or probable myocardial infarction, and 49 of sudden, unattended death. Eighty-seven patients were women and 204 were men. There were 143 deaths. Of every five serious episodes of coronary heart disease three terminated in death during the given episode. The prognosis was better if the patient lived long enough to receive medical attention and still better if he survived the first 24 hours thereafter. Except for those in the category of angina pectoris, most patients had no prior known symptoms of coronary heart disease.