The results of the clinical observations on the 76 cases of the mitral valvular heart disease treated in the Department of Thoracic and Cardiovascular Surgery, Chung-nam National University Hospital during the period of 3 years from June, 1983 to July, 1986, are as follows: l. Of 76 cases, 43 were male and 33 were female with sex ratio of 1.3:1. 2. The age of the patient varied widely from 12 years of the youngest to 60 years of the oldest. 3. The main clinical symptoms on admission were dyspnea on exertion[100%], palpitation[42%], generalized weakness[29%], indigestion[18%], hemoptysis[16%]. 4. The preoperative functional levels according to NYHA classification were class II, III, IV in 9%, 63%, 28% respectively. 5. All 76 patients were operated on under direct vision using extracorporeal circulation, open mitral commissurotomy was done in 15 cases, mitral valve replacement in 37 cases, mitral valve replacement and aortic valve replacement in 11 cases, mitral valve replacement and tricuspid annuloplasty in 8 cases. 6. The operative mortality was 11.8% and results of the operation were good and excellent in 65 cases of survivors.