In 136 consecutive patients who underwent percutaneous transvenous mitral commissurotomy (PTMC) with use of the single rubber-nylon (Inoue) balloon Inoue balloon angiographically analyzed subvalvular fibrosis was assessed retrospectively with regard to results and complications. There were 53 males and 83 females, with a mean age of 22 +/- 11 years (range 10 to 48 years). For the entire group, mitral valve area increased from 0.7 +/- 0.3 to 2.1 +/- 0.6 cm2 (p < 0.001). Valve area increased from 0.7 +/- 0.12 to 1.8 +/- 0.14 cm2 in patients with severe subvalvular fibrosis (n = 55) and from 0.8 +/- 0.11 to 1.9 +/- 0.12 cm2 in cases with mild to moderate subvalvular fibrosis (n = 80; p = NS). The number of patients with 2+ or greater increase in mitral regurgitation was not different between the two groups (6% vs 5.5%, p = NS). None of the patients required mitral valve replacement immediately after PTMC. We conclude that, with use of the Inoue balloon, PTMC can be successfully performed in patients with severe subvalvular fibrosis.