Clinical trials with the Inoue mitral valvotomy balloon have recently begun in the United States. We assessed the effects of 17 demographic, echocardiographic, procedural, and hemodynamic variables on the immediate results, complications, and short-term follow-up of 200 patients in 15 centers undergoing valvotomy with this device. The study population had a mean age +/- SD of 53 +/- 15 years, and the total echocardiographic score was 7.2 +/- 2.4. Valvotomy was technically successful in 96.5% of procedures and increased the mean mitral valve area from 1.0 +/- 0.3 to 1.8 +/- 0.7 cm2 (p less than 0.001); 72% had an increase in valve area greater than or equal to 50%, and 67% had a final area greater than or equal to 1.5 cm2. Major procedural complications included cardiac tamponade during transseptal puncture (1.0%), systemic embolism (1.5%), and severe mitral regurgitation (2.4%); there were no procedural deaths and one hospital death. Multivariate analysis identified the absence of prior surgical commissurotomy and younger age as significant predictors of the gain in mitral valve area, but the correlation coefficients were low. Although the absence of subvalvular disease on echocardiograms was a predictor of a final valve area greater than or equal to 1.5 cm2, the total echocardiographic score did not correlate well with the immediate outcome (r = 0.01, p = NS). No variable was identified as predictive of restenosis, which occurred according to echocardiographic criteria in 14 of 66 (21%) patients evaluated 6 months after valvotomy. Good hemodynamic results with valvotomy were achieved in the majority of patients with low complication rates by many investigators with the use of the Inoue balloon device.(ABSTRACT TRUNCATED AT 250 WORDS)