The results of the clinical observations on the 158 cases of the mitral valvular heart disease treated at the Department of Thoracic and Cardiovascular Surgery, Masan Koryo General Hospital from June, 1986 to December, 1991 were as follows; 1. There were 50 men and 108 women with sex ratio 1: 2.2. 2. The age of patient varied widely from 13 years to 65years. 3. The preoperative functional level accoridng to the NYHA classification were class II, III, IV in 18%, 67%, 15%. 4. All 158 patients were operated on under direct vision using extracorporeal circulation, mitral valve replacement in 118 cases, mitral and aortic valve replacement 40 cases. 5. The follow up period was between 2 months and 65 months postoperatively. [mean 30.1 months] 6. The early operative motality was 5.7%[9 cases], late motality was 4%[6 cases]. 7. The cardiothoracic ratio in the chest X-ray decreased at the 6th month postoperation. [pre-op: 0.60$pm$0.07, post-op: 0.56$pm$0.06 p<0.01]