This is a report of a case in which mitral valve replacement was performed using Starr-Edwards ball valve [model 6230] by total cardiopulmonary bypass with total hemodilution prime and moderate hypothermia. The patient was 21 year old girl, and mitral valvular symptoms occurred 5 years ago. According to clinical features of the disease, the patient was classified as the class IV of N.Y.H. A. cla3sification. The preoperative diagnosis of mitral insufficiency was made mainly by left ventriculography of roentgenologic study. The mitral valve was highly deformed due to scar contraction of valve leaflets and shortening of chordae tendineae. After prosthetic valve replacement, no abnormal hemodynamic signs were observed. The postoperative course was uneventful.[KTCS 1977;1:156-163]