The material studied consists of a group of 274 cases of myocardial infarction seen during, or shortly after, what was considered to be the first attack. The diagnosis was confirmed in every instance by one or more electrocardiograms; in a large majority numerous electrocardiograms were taken, and the diagnosis was based on progressive changes in these records. In only a few cases was a single record obtained, but with the clinical picture the diagnosis was quite certain. These 274 cases have been divided into three groups (table 1). The first or early fatal group consists of 20 per cent (55) of the total number studied, and it is composed of 36 males and 19 females who died within one month of their first clinically recognized myocardial infarction. The second or late fatal group is composed of 49.2 per cent (135) of the total number studied and includes 99 males and