The severity of aortic regurgitation is difficult to estimate prior to mitral valve replacement (MVR) in cases with tight mitral stenosis (MS), because low output state due to mitral obstruction masks signs of aortic regurgitation. This study clarified left ventricular performance, possibly affected by increased diastolic loading after MVR. The study subjects consisted of 12 patients with pure mitral stenosis (MS group) and 11 with combined mitral stenosis and aortic regurgitation (MSAR group). The diagnosis was made by cardiac catheterization preoperatively. The aortographic grade of aortic regurgitation was class 1 or 2 according to the AHA classification. Both groups were matched in terms of severity in mitral obstruction evaluated by mitral valve area. On preoperative echocardiographic evaluation, there was no difference in the mean values of LVDd, LVSd, and %FS between the groups MS and MSAR. After surgery, symptoms improved in each patient. Echocardiography performed three months after MVR revealed no differences in these parameters between both the groups. We concluded that aortic regurgitation evaluated as class 1 or 2 preoperatively does not increase in respect to left ventricular diastolic overloading and echocardiographic left ventricular performance remains unchanged.