To assess the influence of mild mitral regurgitation (MR) on the initial and long-term results of percutaneous mitral valvuloplasty (PMV), the baseline characteristics, early results and follow-up of 102 consecutive patients with mild MR before PMV (group I) were prospectively analyzed and compared with those of 186 consecutive patients without MR (group II). Age, gender and symptomatic status were similar in both groups, but more patients in group I were in atrial fibrillation (70 vs 54%, p < 0.05) and had had a previous episode of pulmonary edema (25 vs 14%, p < 0.05). On echocardiography, patients in group I had larger left atria (58 +/- 12 vs 53 +/- 10 mm, p < 0.05) and more calcified mitral valves (score 1.9 +/- 0.8 vs 1.5 +/- 0.7, p < 0.05), but the total echocardiographic score (8.0 +/- 2 vs 7.3 +/- 2) was similar in both groups. Baseline hemodynamic data were also similar in both groups. On multivariate analysis, group I patients were only independently associated with more calcified mitral valves and larger left atria. PMV success (area gain > or = 50% without complications) was similar (88 vs 86%) in both groups, but mitral valve area gain was smaller (0.8 +/- 0.3 vs 1.0 +/- 0.3 cm2, p < 0.05) in group I. After PMV an increase in the severity of MR > or = 2 grades (17 vs 6%, p < 0.05) occurred more frequently in group II patients.(ABSTRACT TRUNCATED AT 250 WORDS)