Considering the relatively high incidence of severe mitral stenosis in Iran, and for evaluation of the efficacy of PTMC in affected patients, this study was performed on referrals of Shaheed Modarres hospital from 1997 to 1999. The clinical trial and quasi-experimental strategy of this study was performed on 141 patients with signs of dyspnea and MS was diagnosed by echocilfdiography. The patients characteristics, severity of condition, accompanying disorders and valve state were recorded and evaluated. Left and right catheterism were performed for all of the patients and severity of mitral stenosis was classified according to Sellers' method and mitral valve gradient and hemodynamic parameters before and after PTMC were evaluated. For evaluation of aortic failure, aortography was performed and data were statistically analyzed. The age of patients was 37±10 and 82% of them were female and 18% were male. In addition, 26% of them had atrial fibrillation. The area of mitral valve increased from 0.98±0.2 to 1.71±0.2 cm2 (P<0.0001) and its gradient decreased from 16.5±5.5 to 2.7±1.9 (P<0.0001), systolic pressure of pulmonary artery decreased from 49.7±17.9 to 21.5±6.5 mmHg and left atrial pressure decreased from 28±6.6 to 14.4±4.2 mmHg (P<0.0001). In addition, Performing PTMC was successful in 89.5% of patients with MVA≥1.5 cm2 and in 98.5% of patients with gradients less than 6 mmHg. In this respect, all of the patients showed a clear clinical improvement. Cardiac tamponade occurred only in one patient and for one patient with severe mitral failure, an immediate emergency operation was performed. In addition, two of them had atrial fibrillation. There was also no thromboembolic complication and/or death. It is concluded that PTMC is an effective and safe method for the treatment of patients with mitral stenosis and is successful for patients with high pressures in pulmonary artery and accompanied mild to moderate mitral failure. It is recommended to evaluate the long-term consequences of PTMC in patients.