We assessed immediate and late outcome in 55 patients with significantly calcified valves (group 1) after balloon mitral valvotomy and compared the results with those from 60 patients with noncalcified or minimally calcified valves (group 2). After valvotomy, mitral valve area increased from 1.03 +/- 0.30 cm2 to 1.64 +/- 0.35 cm2 (p = 0.0001) by echo planimetry in group 1 but was significantly smaller than the mitral valve area in group 2 after valvotomy (1.94 +/- 0.38 cm2; p = 0.0001). At a mean follow-up period of 30 months (range 2 to 81 months), 51% of patients in group 1 and 83% in group 2 were symptom free (p = 0.0002). In group 2, 15 (27%) patients and in group 2, 4 (7%) patients had cardiac events (p = 0.003). The risk ratio for cardiac events was 4.3 times greater in group 1 than in group 2. In group 1, the risk ratio for cardiac events was 3.2 times higher in patients age > or = 65 years and in patients with atrial fibrillation. The 6-year cumulative cardiac event-free survival rate was 64% in group 1 and 90% in group 2 (p = 0.005). In 75 (65%) patients who had follow-up echocardiographic study (35 in group 1 and 40 in group 2), mitral valve area decreased to 1.48 +/- 0.42 cm2 at follow-up in group 1 (p < 0.01) and to 1.77 +/- 0.50 cm2 in group 2 (p = 0.3). Restenosis occurred in 16 (46%) of 35 patients in group 1 and 10 (25%) of 40 in group 2 (p = 0.06).(ABSTRACT TRUNCATED AT 250 WORDS)