We are not the first to attempt repair of left ventricular rupture complicating mitral valve replacement, as 18 analogous cases have been reported earlier in the literature. Our series comprises 8 patients, 5 of who, survived. A review of these 26 cases provided several facts of interest to surgeons dealing with this complication. The rupture occurred either as a laceration in the posterior atrioventricular groove (type I, 16 of 26 patients) or as a perforation of the midportion of the left ventricle (type II, 10 of 26 patients). Intraoperative rupture (17 of 26 patients) was usually detected on termination of bypass, whereas delayed rupture (9 of 26 patients) occurred after chest closure or in the recovery room. The morality rate was about 50 per cent for the intraoperative type, and no patient survived a delayed rupture. The prognosis appeared to be most in intraoperative type II lesions. The main factors affecting the prognosis were (1) instant reinstitution of extracorporeal circulations and (2) avoidance of the circumflex coronary artery during repair of type I lesions located close to the anterolateral mitral commissure. Attempts to suture a ventricular rupture on the pressure-loaded, beating heart were always unsuccessful and frequently extended the laceration. Patients with the delayed type of rupture died of hemorrhage before they could again be placed on bypass. It may be preferable to reopen the lefr atrium in order to repair a type I laceration. In type II perforations, direct repair with buttressed sutures should be attempted from the exterior of the heart. The angulated metal cannula for drainage of the left ventricle was identified as a possible, but not previously reported, cause of myocardial perforation. It is hoped that the use of a soft cannula or a metal cannula with an angle of 60 degrees instead of 90 degrees will reduce the incidence of this complication.