Late results after successful percutaneous mitral commissurotomy were assessed by prospective clinical and echocardiographic follow-up. Fifty-seven patients were followed for a mean of 19 +/- 6 months (range 9 to 33) after the procedure. Mitral valve area (measured by Doppler half-time method) increased from 1.0 +/- 0.2 to 2.2 +/- 0.5 cm2 immediately after commissurotomy, and then decreased to 1.9 +/- 0.5 cm2 at follow-up (p less than 0.05), whereas gradient did not change after its immediate postcommissurotomy reduction. Echocardiographic restenosis (mitral valve area less than or equal to 1.5 cm2 with greater than 50% reduction of initial gain) was seen in 12 of 57 patients (21%). Atrial shunting, detected by transthoracic color Doppler in 61% of patients immediately after the procedure (color flow jet through atrial septum), persisted in 30% at follow-up. Restenosis by univariate analysis correlated with age, smaller valve area after the procedure, and higher echocardiographic score. Multivariate analysis identified leaflet mobility and calcifications as the components of a score that was predictive for restenosis. Magnitude of shunt (pulmonary-to-systemic flow ratio greater than 1.5), use of a Bifoil balloon (2 balloons on 1 shaft), and smaller valve area after the procedure were predictors by multivariate analysis of the persistence of atrial shunting. Clinical improvement persisted at long-term follow-up (mean New York Heart Association class 1.6 +/- 0.6 vs 2.6 +/- 0.6 before commissurotomy). Improvement of greater than or equal to 1 functional class was seen in 75% of patients (80% of those without and 58% of those with restenosis); patients with a shunt did not differ from the entire group.(ABSTRACT TRUNCATED AT 250 WORDS)