This study evaluated the effects of balloon mitral valvuloplasty (BMV) on exercise capacity and skeletal muscle structure and function in 10 subjects with mitral stenosis (mean age +/- SD 33 +/- 5.5). Measurements were obtained before, and 2 weeks and 4 months after BMV to provide baseline data, to examine the effects of improved hemodynamics, and to examine the effects of resumption of normal physical activity, respectively. Valvuloplasty caused an increase in mitral valve area (0.89 +/- 0.04 to 1.75 +/- 0.07 cm2; mean +/- SE), and an increase in resting cardiac output (3.8 +/- 0.18 to 4.6 +/- 0.19 L/min, p < 0.05). At early follow-up after 2 weeks, subjects did more work (31% increase, p < 0.01) and had greater maximal oxygen consumption (11% increase, p < 0.01). However, measurements reflecting skeletal muscle histology, biochemistry, and function were unaltered at this stage. Four months after BMV, subjects had a further increase in exercise capacity compared with both baseline (58% increase, p < 0.01) and early follow-up (20% increase, p < 0.05). There were associated late increases compared with baseline in quadriceps cross-sectional area (66 +/- 5.8 vs 61 +/- 5.5 cm2, p < 0.05) and torque production (125 +/- 14 vs 118 +/- 16 Nm, p < 0.05). The percentage of slow twitch type I fibers increased compared with baseline (41 +/- 2.0% vs 33 +/- 3.1%, p < 0.05), as did the size of type II fibers (5.9 +/- 0.49 vs 4.9 +/- 0.57 microns2 x 10(3), p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)