The authors report on two children who underwent valve replacement. Case 1: A 10-year-old boy with high fever and severe heart failure was diagnosed as having aortic regurgitation and left ventriculo-right atrial fistula caused by active infective endocarditis. An aortic annular defect was repaired by a pericardial patch to enlarge the aortic annulus followed by aortic valve replacement with a 17-mm Björk-Shiley prosthetic valve. He is doing well 2 years after surgery. Case 2: A 3-year-old girl was diagnosed as having congenital mitral stenosis with severe pulmonary hypertension. Mitral valve stenosis was a commissural fusion type according to the Carpentier's classification. An open mitral commissurotomy was attempted initially, resulting in severe mitral regurgitation. Then, the mitral valve was replaced with a 16-mm CarboMedicus bileaflet valve. Her postoperative course was uneventful and residual pulmonary hypertension decreased gradually. The selection of prosthetic valves is important in its type and size in order to obtain as large an orifice as possible. Careful postoperative follow-up is mandatory.