During five years or until death, we had under observation 74 patients who survived the acute phase of myocardial infarction, 66 patients with angor inestable, and a third group, also of 66 patients of the coronary unit, but whose cases didn't show evidence of their illness being due to myocardial infarction. The general features were similar in the three groups. The patients outliving myocardial infarction reached 69%; those surviving angor inestable, reached 79%, and the survivors of the no-coronary group, 92.5%. There were not significant differences among the three groups in mortality rate due to non cardial illnesses. The differences are in relation with sudden death; in the first groups, 14.8%, 10.6% in the second group, and only 1.5% in the third one. In the coronary groups half the total mortality was due to sudden death. Death was instantaneous in 26% of the cases and 52% occurred in less than two hours. All of these sudden deaths occurred out of the Hospital. Patients with antecedents of previous myocardial infarction showed from 3 to 6 more sudden deaths than those patients suffering a first myocardial infarction. The myocardial infarction patients who developed cardiomegaly afterwards registered two and a half more sudden deaths than those without cardiomegaly. Differences were highly significant; 28.5% sudden deaths in those patients with cardiomegaly and 8.4% in patients without cardiomegaly. These results show that the higher rate of sudden deaths is due to a more extensive myocardial damage. Arterial hypertension also constitutes and important risk of sudden death, even when it is properly controlled after the acute period.