PURPOSE To demonstrate the importance of the preservation of mitral annulus-chordae tendineae-papillary muscles continuity in mitral valve replacement. METHODS We studied 21 patients who were submitted to mitral valve replacement, divided in two randomized groups: group 1, 12 cases who undergone mitral valve replacement, with preservation of the posterior leaflet and correspondent chordae tendineae; and group 2-9 cases who undergone conventional mitral valve replacement, excising the mitral valve apparatus. The left ventricular function was studied both, in the pre and post operative period, by echocardiography, cardiac catheterization, and radioisotopic study. The statistical analysis was done by the Wilcoxson's test. RESULTS There were no early post operative deaths. Analyzing the results of the ejection fraction by the radioisotopic study we found a significant difference (p = 0.03) between the percentual decrease of the two groups. The results of the fractional shortening were higher in group 1 than in group 2, however not significant. The left ventricular diastolic diameters average was lower in group 1 than in group 2, so as the left atrium diameter. We found a decrease in left ventricular end-diastolic pressure in group 1, however there was an increase in group 2, by the cardiac catheterization. There was a proportional increase in group 1 both in lung artery and lung capillary pressures. There was a significant difference (p = 0.05) between the average values of right ventricular diastolic pressure. CONCLUSION There is better preservation of left ventricular function in group 1.