The purpose of this study was to determine the immediate effect of percutaneous mitral commissurotomy (PMC) on left ventricular (LV) performance. We studied 30 patients with severe mitral stenosis undergoing successful PMC by cardiac catheterization and angiography before and 5 minutes after PMC. All patients were in sinus rhythm and no patient had hypertension or clinical coronary artery disease. We conclude that the left ventricular end-diastolic volume and the stroke volume increased significantly immediately after PMC because of and increase in LV filling after relieving the mitral mechanical obstruction.