We evaluated 68 patients with mitral valve disease who underwent mitral valve replacement from April, 1986, to December, 1988. Among them 20 patients showed increased systolic pulmonary arterial pressure greater than 60 mmHg and postoperative hemodynamic data were obtained in 19 patients average 13 months after mitral valve replacement. The results were as followings. 1. Average pulmonary systolic pressure decreased from 84.8$pm$4.5 preoperatively to 33. 0$pm$1.9mmHg postoperatively[P<0.001]. 2. Average pulmonary vascular resistance index decreased from 1425$pm$148 preoperatively to 287+35.8 dyne * sec * cm2 * m postoperatively[P<0.001]. 3. Average cardiac index rose from 1.927$pm$0.169 preoperatively to 2.625$pm$0.159 L/min/m2 postoperatively [P <0.005]. This study shows that pulmonary hypertension and the increased pulmonary vascular resistance index due to mitral valve disease can regress significantly after mitral valve replacement