Percutaneous mitral commissurotomy using balloon catheters was attempted in 17 patients (16 of whom were women) with rheumatic mitral valve stenosis. The patients' age ranged from 15 to 34 years (men 21 years). Functionally, 15 of the patients were in stage III of the New York Heart Association classification, and 2 were in stage II. Sinus rhythm was present in all cases. Slight mitral regurgitation was noted in 2 cases, associated with mild aortic disease in one of them; 3 other patients presented with slight aortic regurgitation. In all 17 cases the mitral stenosis was tight, uncalcified, with flexible valves and little or no alteration of the subvalvular system. One single balloon catheter was used in 11 patients and 2 balloon catheters were introduced simultaneously in the remaining 6 patients. The new therapeutic method was successful in all patients. Following valvuloplasty, the mean transmitral gradient was reduced from 25 +/- 3 to 11 +/- 2 mmHg (P less than 0.001), the mean capillary pressure fell from 26.8 +/- 7.1 to 13.5 +/- 3.7 mmHg (P less than 0.001) and the cardiac index increased from 3.3 +/- 1 to 4.2 +/- 1.2 l/min/m2 (P less than 0.001). The mitral valve area, measured by two-dimensional echocardiography, increased from 1.0 +/- 02 to 2.1 +/- 0.3 cm2 (P less than 0.001). The mitral valve regurgitation observed in 2 patients before valvuloplasty was aggravated, although still moderate, in one of them and remained stable in the other.