Bet een November 1991 and December 1993, twelve patients (Male: 2, Female: 10) who had mitral valve disease without primary pulmonary disease underwent mitral valve replacement. The pulmonary function test (PFT) was performed preoperatively and postoperatively (mean, 9 months after operation). Mitral valve replacement was indicated for mitral stenosis in 9 patients and for mitral insufficiency in 3 patients. Preoperative WHh functional class were 111 in 11 patients and class rV in 1 patient. Postoperatively, ten patients (83 %) were classified into NYHA functional class 1. There was a significant decrease in cardiothoracic ratio (CTR) postoperatively (p< 0.05). The pulmonary function before operation was low compared with predicted values in vital capacity (VC) and forced mid-expiratory flow (FEF 25∼75 %). The FEF 25%-75% and maximal voluntary ventilation (MW) were low compared with predicted values postoperatively. There was no significant difference in the pulmonary function before an after op- eration. Twelve patients were divided into 2 groups according to the early postoperative NYHA functional class. In class I group, the postoperative pulmonary function was significantly improved in 6 parameters (RV, FRC, TLC, FEVI , FEVI /FVC, and FEF 25∼75%), but in class ll group, there was no significant change in the pulmonary function after operation.