Forty two cases of complete or incomplete rupture of the free left ventricular wall were reviewed in a group of 136 patients who died of acute myocardial infarction in a Coronary Care Unit and who underwent autopsy examination over a 30 month period. Four groups were distinguished on macro and microscopic features of the rupture based on a previously defined classification established by former studies: type I rupture (13 cases) with an almost direct trajectory with little dissection and bloody infiltration of the myocardium; type II (13 cases) with a multicanalicular trajectory and widespread myocardial dissection and bloody infiltration; type III (9 cases) in which the orifice of rupture is protected by an intraventricular thrombus or a pericardial symphysis; type IV (7 cases) with incomplete epicardial, endocardial or intramyocardial rupture which never was transparietal. The clinical characteristics (age, sex, time interval before admission to the coronary care unit, previous history, ECG location of the myocardial infarcts, clinical course, Killip classification, treatment and ECG changes) and anatomical findings (weight of the heart, presence of haemopericardium, previous infarction or aneurysm, location of the infarct, presence of intraventricular thrombus or ventricular septal defect, number of vessels with over 75 p. 100 obstruction and topographical location of the rupture) were compared. The type I ruptures had smaller infarcts and a quicker terminal illness with rapid evolution to cardiac tamponade. In type II ruptures, the infarcts tended to be bigger, sometimes associated with septal rupture and the terminal illness was longer lasting than in the previous group, reflecting a longer evolution towards cardiac tamponade.(ABSTRACT TRUNCATED AT 250 WORDS)