Author compared the effect of surgical methods between 40 patients who received mitral valve replacement with complete excision of the mitral valve[resected group] and 41 patients who received mitral valve replacement with preservation of posterior chorda tendineae and posterior mitral leaflet[preserved group] from 1985. 2. to 1989. 4. at cardiothoracic department of Pusan National University Hospital.v 1. There was no significant difference between the preserved group and resected group in cardiopulmonary bypass time and aortic cross clamping time and NYHA classification. 2. In preserved group of Mitral stenosis and Mitral regurgitation, the left ventricular functions were much improved after mitral valve replacement than resected group, but there was not so difference between the preserved group and reserved group in Mitral steno-regurgitation. 3. There were remarkable decrease in complication rate in preserved group compared to resected group. And also the death rates were remarkably decreased in preserved group which was 4.9% compared to resected group which was 17.5%. As the preservation of the posterior mitral leaflet and chorda tendineae during mitral valve replacement in mitral valve disease showed significantly improved effects in the maintaining of left ventricular function and reducing the postoperative complication, I assume the preservation of posterior mitral leaflet and chordae during mitral valve replacement will bring better result.