In order to evaluate the effectiveness and risks of percutaneous mitral commissurotomy (PMC), we tried this procedure in 130 patients. Nine attempts were unsuccessful due to pre-PMC complications (haemopericardium 2, air embolism 1) or to technical failure (6 cases, 5 of which occurred in the first 15 attempts). PMC could be performed in 121 patients: 88 women and 33 men aged from 13 to 79 years (mean 42 + 15 years); 22 patients had previously been operated upon, 5 had a history of embolism, 99 were in functional stage III or IV. Echocardiography divided these patients into 3 groups: 29 had calcified leaflets (group 1), 42 had flexible leaflets and little alteration of the subvalvar system (group 2), and 49 had flexible leaflets with alteration of the subvalvar system (group 3). Mitral regurgitation grade 1/4 was present in 32 cases. PMC was performed with one balloon (Trefoil 3 x 12 mm) in 14 patients and therafter with two balloons (Trefoil 3 x 10 mm plus conventional 15 or 19 mm balloon) in 107 patients. PMC resulted in significant improvement in haemodynamic values: the mean capillary pressure fell from 20 +/- 7 to 11 +/- 5 mmHg (p less than 0.0001) and the mean mitral gradient from 16 +/- 6 to 6 +/- 2 mmHg (p less than 0.0001), while the cardiac index rose from 2.7 +/- 0.6 to 3.1 +/- 0.7 l/mn/m2 (p less than 0.001) and the mitral valve area (MVA) from 1.1 +/- 0.2 to 2.2 +/- 0.5 cm2 (p less than 0.0001).(ABSTRACT TRUNCATED AT 250 WORDS)