Thirty-seven patients with symptomatic mitral stenosis underwent balloon dilatation of the mitral valve. Significant increases (p < 0.001) were noted in both catheterization- and Doppler-determined valve area (0.9 ± 0.3 to 1.8 ± 0.8 and 0.9 ± 0.2 to 1.7 ± 0.5 cm 2). However, catheterization and Doppler areas before and after valvuloplasty correlated less well (r = 0.51, p < 0.002 and r = 0.47, p < 0.005, respectively) than the catheterization-Doppler area correlation in a previous study of 59 consecutive patients with varying degrees of mitral stenosis (r = 0.84, p < 0.001). Mitral valve area increases were independent of valve thickness estimated using 2-dimensional echocardiography. Flail mitral leaflet movement was not observed and the degree of mitral regurgitation qualitatively assessed using pulsed Doppler mapping techniques increased by >1 of 4 grades in only 1 patient. The lateral mitral valve orifice diameter increased more than the anteroposterior diameter, suggesting commissural splitting as the mechanism of successful valvuloplasty. Increases (all p < 0.0001) were noted in mitral valve EF slope (7 ± 5 to 18 ± 10 mm/s), excursion (11 ± 5 to 13 ± 4 mm), S20S interval (0.07 ± 0.02 to 0.08 ± 0.02 s) and cardiac output (4.2 ± 1.3 to 5.3 ± 2.0 liters/min). There were significant decreases (all p < 0.001) in left atrial diameter (5.4 ± 1.0 to 5.1 ± 1.0 cm), mean catheterization gradient (15 ± 5 to 8 ± 4 mm Hg) and mean Doppler gradient (10 ± 4 to 6 ± 3 mm Hg). Thus, while Doppler study can accurately predict catheterization mitral valve area in patients referred for assessment of mitral stenosis, the correlation coefficients are lower in balloon valvuloplasty patients preselected for severe mitral stenosis and in patients after balloon valvuloplasty. Other noninvasive parameters, previously shown to be inaccurate predictors of baseline valve area, do reflect increases after valvuloplasty. Valvuloplasty can successfully increase valve area even in patients with severe mitral valve thickening and causes little change in the degree of mitral regurgitation.