Mortality in the early phase of acute myocardial infarction occurs both during the pre-hospital period and after admission to the Coronary Care Unit. This report is an analysis of deaths that occurred in the Coronary Care Unit within a 3 year period. Forty percent of 304 patients (13 percent) unth. acute myocardial infarction died in the Coronary Care Unit, Fifty percent of the deaths were due to cardiac arrhythmias and 45 percent attributable to myocardial pump failure. Mean delay in hospital admission from onset of symptoms was 15 hours. Factors affecting early mortality and their prevention are discussed.