A hundred and eleven patients of mitral valvular heart disease, who were operated at Seoul National University Hospital, were analysed with echocardiogram before and after operation during the period from November 1979 to February 1982. Twenty-eight patients had mitral stenosis and eighty-three mitral regurgitation. In patients with mitral stenosis, right ventricular end-diastolic volume was in normal range at preoperative and postoperative period. But the left ventricular end-systolic volume was slightly increased preoperatively to 35.4mm and decreased to 33.5mm on immediate postoperative period and 32.5mm after a year later. The left ventricular end-diastolic volume was 50.5mm preoperatively and fell to 46.8mm postoperatively. Ejection fraction was normal preoperatively and postoperatively without changes. Left atrial size fell significantly from 50ram to 37.6mm at the time of late follow-up study. With mitral regurgitation, right ventricular end-diastolic volume was also normal preoperatively and postoperatively. The left ventricular end-systolic volume was increased to 41.9mm and decreased to 31.6mm postoperatively with statistic significance. Left ventricular end-diastolic volume fell from 58.5mm to 45.7mm significantly at the time of late follow-up period. Ejection fraction was also within normal range and had no changes postoperatively. Left atrial size fell from 54.8mm to 45.5mm on a year later [ p value less than 0.01 ]. When atrial fibrillation, the left atrial dimension was increased as 54.9mm compared with 46.8mm of no atrial fibrillation patients. [KTCS 1983;1:55-64]