MANY PATIENTS with myocardial infarction or angina pectoris, or both, have been noted to have high hematocrits, particularly patients in the younger age groups. In fact, erythrocytosis occurred frequently enough in patients with myocardial infarction to warrant a systematic study of this problem. Material and Methods The material for this study was obtained from autopsy records of the Veterans Administration Hospital in New Orleans. One hundred patients with acute myocardial infarction were selected at random. Patients with associated diseases known to affect the hematocrit, i.e., carcinoma, uremia, pulmonary disease, and polycythemia vera, were excluded from this study. The hematocrit values obtained on the day of admission were recorded for each patient. Ninety-two of the 100 patients had more than one admission to the Veterans Administration Hospital. Hematocrit values were available for these patients for periods ranging from 11 years to 2 months before the last hospital admission. Since there was