In 4 children (2.4-10.9 y.o) with mitral valve regurgitation, prosthetic valve replacement was done using warm heart surgery. Three of them had previously received 1-3 times valve repair operations and the other one was accompanied by endocarditis. The condition of 3 children were in NYHA grade 4 and received dopamine preoperatively. At the esophageal temperature of 34 degree, aorta was cross clamped for 79-216min. with continuous coronary perfusion of 3ml/kg/min, however, no child showed postoperative low output syndrome, and the maximum use of dopamine was 2-6μg/kg/min and the CK-MB at 1POD was within the normal range in all cases. Warm heart surgery showed better myocardial protection for pediatric mitral valve replacement.