To determine whether the presence of an aneurysmatic (severely enlarged) left atrium (greater than 60 mm on echocardiography) influences results of percutaneous mitral valvuloplasty (PMV), the clinical, echocardiographic and hemodynamic characteristics and the results of this technique were compared in 46 consecutive patients with aneurysmatic left atrium (group I) and 125 consecutive patients without such echocardiographic finding (group II). Left atrial size was 70.5 +/- 8 vs 50.1 +/- 6 mm (p less than 0.005) in groups I and II, respectively. Patients in group I were older (57 +/- 12 vs 48 +/- 12 years, p less than 0.025), more symptomatic (New York Heart Association functional class greater than or equal to III or IV: 67 vs 42%, p less than 0.05), and had atrial fibrillation more frequently (91 vs 44%, p less than 0.001). The echocardiographic score (8.9 +/- 1.9 vs 7.5 +/- 2, p less than 0.005) and the incidence of mild mitral regurgitation on angiography before PMV (54 vs 30%, p less than 0.01) was also higher in group I patients. Hemodynamic parameters before PMV were similar in both groups, but after the procedure, final mitral valve area (1.61 +/- 0.5 vs 1.95 +/- 0.4 cm2, p less than 0.05) and the absolute increase in mitral area (0.81 +/- 0.3 vs 1.02 +/- 0.3 cm2, p less than 0.05) were lower and mean pulmonary artery pressure (35 +/- 10 vs 28 +/- 9 mm Hg, p less than 0.025) was higher in group I.(ABSTRACT TRUNCATED AT 250 WORDS)