To detect the genesis and the prognosis of left ventricular failure (LVF) following the valve replacement surgery to mitral stenosis (MS), preoperative values and postoperative courses were assessed in 90 patients with MS. The criteria for LVF were as follows: postoperative severe left ventricular (LV) dysfunction which required intra-aortic balloon pumping (IABP) support with large doses of catecholamine. Among these 90 patients, LVF had occurred in 13 patients, of which 6 had a definite cause of LVF (group A), but the other 7 patients failed to LVF despite uneventful operation (group B). Comparing the pre- and postoperative values in these two groups, the duration of IABP support was much longer in group A, and the weaning rate from IABP was also poor in this group. Long-term survival was achieved only by one patient in group A, whereas 5 out of 6 patients of group B survived long-term postoperatively. Evaluating the preoperative LV function in group B patients, depressed LV function [%fractional shortening (%FS) less than or equal to 27%] was observed in 5 patients. Among these 5 patients, three had low cardiac output; in other two, preoperative %FS was severely depressed. In such patients, the responses to preoperative dobutamine administration tests were poor, and the values of %fibrosis of the LV myocardium, which was demonstrated by intraoperative biopsy, was greater in them. In conclusion, the causes of postoperative LVF following the mitral valve replacement to MS was divided into two categories: one due to perioperative complication and another due to preoperatively impaired LV function.(ABSTRACT TRUNCATED AT 250 WORDS)