During a 30-month period, 51 patients underwent mitral valve replacement. There were 3 hospital deaths (5.9%), 2 of which were due to ventricular rupture. The 3 patients who died were among 13 patients in whom mitral valve replacement was combined with tricuspid or aortic valve operation or both. Postmortem findings in the 2 patients who died of ventricular rupture showed that the ventricular tears were located between the atrioventricular groove and the unresected papillary muscle stumps, in an area of ventricle formerly tethered by the posterior chordae tendineae. In the last 14 patients in the series, the posterior leaflet of the mitral valve and its chordae tendineae were left intact, and there was no mortality or prosthetic valve dysfunction. In patients with myxomatous or ischemic disease, the posterior leaflet was left completely intact. For patients with fibrocalcific rheumatic disease, we have developed a technique of partial excision and debridement of the posterior leaflet, preserving the intermediate and basal chordae tendineae attachments. With the techniques described, preservation of all or part of the posterior leaflet and its chordae tendineae does not appear to interfere with prosthetic valve function and, by reducing the risk of ventricular rupture, should enhance survival after mitral valve replacement.