To evaluate the efficacy of percutaneous balloon valvuloplasty in patients with prior surgical mitral commissurotomy, balloon valvuloplasty was performed in 9 patients with restenosis 14.1±9.3 years(5-30) after the operation. There were 6 women and 3 men with a mean age of 43±8 years. Two patients were in NYHA class II, 6 in classIII and 1 in class IV. Six were in atrial fibrillation. Percutaneous balloon mitral valvuoplasty in 9 patients resulted in increase of mitral valve area(1.03±0.13 to 1.81±0.49cm², P<0.05) by Gorlin's formula, and decrease of mean diastoic mitral pressure gradient(13±5 to 6±2 mmHg, P<0.05), and mean left atrial pressure(17±7 to 10±4 mmHg, P<0.05). And also cardiac output increased(4.2±0.8 to 4.6±1.0L/min, P<0.05) and mean pulmonary artery pressure and pulmonary vascular resistance decreased(25±6 to 19±5 mmHg, P<0.05, 316±103 to 239±101 dyne·s·cm^-5, P<0.05). Mitral regurgitation develop or increased in severity in 2 patients. No other complications occured.