Three cases of rupture of the interventricular septum occurring coincident with acute inferior myocardial infarction are reported and the relevant literature is reviewed. One patient under-went successful surgical repair and, in addition, had an aneurysmectomy. Clues and pitfalls in diagnosis as well as the possible confusion with ruptured papillary muscle are discussed. Due to a dual blood supply to the interventricular septum, rupture occurs most often in the setting of advanced, diffuse coronary artery disease. Hypertension or other factors may be of lesser importance. Early surgical approach is advocated and may of necessity include infarctectomy, aneurysmectomy, and coronary artery by-pass surgery in addition ot repair of the ruptured interventricular septum. Use of an intraaortic balloon counterpulsator may prove to be of considerable help in the preoperative and postoperative management of these patients.