The benefits of surgical correction of mitral incompetence were assessed in 51 patients by comparing pre and postoperative catheter and quantitative angiographic results. The mean age of the patients was 43.5 +/- 12.3 years. The mitral lesions were elongation or ruptured chordae (27 cases), valvular perforation due to endocarditis (1 case) and the usual rheumatic disease in 23 cases. Hemodynamic investigation was carried out on average 2 months before operation and 29 +/- 22 months after surgery. The following angiographic parameters were measured : indexed end diastolic and end systolic volumes (EDV and ESV), ejection fraction (EF), myocardial mass (MM) and its ratio to EDV (hypertrophy coefficient : HC) and the geometry of the ventricle as assessed by diastolic and systolic coefficients of excentricity (DE and SE). Surgery comprised 13 mitral valvuloplasties and 38 valve replacements. Patients who suffered perioperative myocardial infarction or who had a residual valvular lesion were excluded from the study. After surgery, the hemodynamic state was considerably improved with a significant decrease in pulmonary capillary pressures (11 +/- 5 compared to 17 +/- 6 mmHg, p less than 0.09) and mean pulmonary artery pressures (19 +/- 7 compared to 27 +/- 11, p less than 0.01) and increase in cardiac index (2.8 +/- 0.7 compared to 2.3 +/- 0.6 l/min/m2, p less than 0.01). There was an associated decrease in ventricular volumes (EDV : 115 +/- 44 compared to 165 +/- 43, p less than 0.01) (ESV : 60 +/- 39 compared to 77 +/- 22, p less than 0.001). The reduction in myocardial mass was less spectacular (129 +/- 40 compared to 148 +/- 32, p less than 0.01) with a resulting increase in the HC (1.10 +/- 0.26 compared to 0.88 +/- 0.17, p less than 0.001). The geometry of the LV was less spherical in diastole (DE 0.76 +/- 0.08 compared to 0.70 +/- 0.08, p less than 0.001) and in systole (SE = 0.83 +/- 0.06 compared to 0.77 +/- 0.08, p less than 0.001). The EF fell slightly but this was not statistically significant (0.51 +/- 0.13 compared to 0.53 +/- 0.09 NS). The surgical result of 14 patients with PCP greater than or equal to 13 mmHg was considered hemodynamically incomplete, and this was confirmed by a lower cardiac index than in the remaining 37 patients (2.4 +/- 0.5 compared to 3.0 +/- 0.7, p less than 0.01).(ABSTRACT TRUNCATED AT 400 WORDS)