The paper reports on the study of 1457 patients with acute myocardial infarct (Ami) admitted in the word of the cardiac intensive care of the clinic for 10.5 years. The general mortality was of 21.2% and the sudden death (defined as such when appeared suddenly within less than 1 hour from the onset of the acute symptoms, but after 24 hours from the onset of AMI in a patient apparently equilibrated) appeared in 114 patients who were examined postmortem (43.3% of the total of the deaths). The main causes of the SD was rupture of the myocardium (28.8% of the general mortality), primary ventricular fibrillation (22.0%) and thromboembolic phenomena (17.8%). The sudden death by rupture of the myocardium appeared in a first AMI, usually large and was not helped by the anticoagulant treatment or by other therapy. Primary ventricular fibrillation appeared during the first week from the onset and was favoured by the ventricular hyperexcitability and active myocardial ischemia (which were not specific). Xyline (only more than 2 mg/min) and amiodarone gave a good protection. The sudden death by systemic thromboembolization appeared almost only in the antero-lateral myocardial infarcts, 5-8 days after the onset. The appearance of a small flow syndrome "sine materia" with or without association of some recurrent arrhythmias was suggested. Efficient anticoagulation prevented systemic thromboembolization and, to a smaller extent to pulmonary thromboembolization.