To evaluate the effect of mitral valve repair on the regression of left ventricular mass, we studied 50 consecutive patients with severe, pure mitral regurgitation undergoing mitral valve repair. Two-dimensional echocardiograms were recorded a mean 2.5 +/- 2.0 weeks before and 6.5 +/- 2.5 months after valve operation. Postoperative significant mitral regurgitation was present in 3 patients. After mitral valve repair there were significant decreases in left ventricular end-diastolic volume index (133 +/- 39 mL/m2 to 79 +/- 35 mL/m2; p < 0.001), end-systolic volume index (44 +/- 26 mL/m2 to 30 +/- 26 mL/m2; p < 0.001), stroke volume index (89 +/- 29 mL/m2 to 49 +/- 19 mL/m2; p < 0.001), and mass index (211 +/- 82 g/m2 to 134 +/- 52 g/m2; p < 0.001). There also were significant decreases in left atrial dimension (47 +/- 9 mm to 38 +/- 9 mm; p < 0.001), left ventricular end-diastolic dimension (61 +/- 8 mm to 48 +/- 7 mm; p < 0.001), and end-systolic dimension (39 +/- 8 mm to 32 +/- 7 mm; p < 0.001). Left ventricular ejection fraction decreased slightly from 0.69 +/- 0.12 to 0.64 +/- 0.12; p < 0.01) after repair. Thus, correction of pure mitral regurgitation leads to reduction of the cardiac chamber size and left ventricular volumes as well as regression of the left ventricular mass.