BACKGROUND: Mitral stenosis (MS) and mitral regurgitation (MR) have different pathophysiologies and left ventricular function after miral valve replacement (MVR) in both diseases has been well known. However, there has been no report comparing the change of right ventricular (RV) function immediately after MVR. We evaluated the change of RV function following MVR in MS and MR using a RV ejection fraction (RVEF) thermodilution catheter. METHODS: With IRB approval, 27 patients with MS and 22 patients with MR undergoing MVR were included. Patients with tricuspid regurgitation were excluded. A RVEF catheter was inserted before the induction of anesthesia. Hemodynamic parameters were measured after anesthesia (T1, control), immediately after the termination of cardiopulmonay bypass (T2) and after the sternum was closed (T3). RESULTS: Pulmonary capillary wedge pressure (PCWP) and end systolic and end diastolic RV volume index (RVESVI and RVEDVI) were higher in MS than in MR and there was no difference in RVEF at T1. Heart rate increased and mean pulmonary artery pressure (mPAP), PCWP, and pulmonary vascular resistance significantly decreased at T2 in both groups. RVEF increased and RVESV and RVEDV decreased significantly only in MS after MVR versus that at T2. There was no difference in hemodynamic parameters between both groups at T2 and T3. CONCLUSIONS: RV function was significantly improved in MS but not in MR after MVR. However, there was no significant hemodynamic difference between MS and MR after MVR, though they are known to have different preoperative pathophysilogies and postoperative left heart functions.