Between 1979 and 1988 four fatal cases of left ventricular disruption after mitral valve replacement were registered among 332 patients submitted to mitral valve replacement, with two different types of porcine prosthesis in isolated or combined operations. All patients were elderly women (mean age 58) with predominant mitral insufficiency. Complications occurred after isolated MVR in 3 patients and in 1 patient after MVR combined with coronary artery by-pass. Damage appeared to have been caused by rhythmical pulling exerted by sorrounding myocardium against a hypocinetic ventricular wall locally ischemic by compression of a viciously positioned prosthesis. The mis-evaluation of the mitral annulus was induced by the usage of innadequate sizers used in profoundly relaxed heart under cardioplegia. The profile of the prosthesis probably influenced the type of lesion. Modifications in the sizer's head and the usage of flexible and malleable sizer-holders, that could permit a more accurate position of sizer's head in the mitral annulus are suggested. Possible etiological co-factors are: elderly patients, particularly women, with myocardial lesions secondary to overzealous resection of papillary posterior muscle or of the mitral cusp, and the loss of the internal buttress of the myocardium after resection of subvalvar apparatus (untethered ventricle). Preserving chordae tendinae of the annulus of mural leaflet could help the prevention of these complications.