The mortality from acute myocardial infarction has remained unchanged over the past three decades. The records of 200 patients hospitalized because of acute myocardial infarction were analyzed at St. Paul's Hospital, Vancouver. Criteria for diagnosis were autopsy evidence and electrocardiographic evidence of acute muscle necrosis. Sixty-two patients died, 30 in the first three days and 41 in the first week; 33 of these deaths were due to cardiac arrhythmias, cardiac arrest or hypotension. Anticoagulants improved the mortality, but the degree of control was not a factor. Thromboembolism was significantly decreased by anticoagulants. Forty-nine patients died in shock; pressor amines did not improve the mortality in such cases. This study emphasizes the need for intensive care during the early critical period of the illness. Prompt adequate therapy of shock may improve the prognosis.