A neonate and an early infant with critical aortic stenosis successfully underwent open commissurotomy and resection of dysplastic myxomatous tissue on the leaflet edges using cardiopulmonary bypass. Case 1: A 31-day-old boy admitted to our unit with shock. Echocardiography demonstrated critical aortic stenosis and severe left ventricular dysfunction (EF = 15%). Case 2: A 12-day-old boy suddenly deteriorated and required resuscitation with ventilation and inotropic support. Emergency operation was required in both cases using cardiopulmonary bypass with systemic hypothermia (30 degrees C). In both cases, the aortic valve was bicuspid and dysplastic with gelatinous myxomatous tissue on the leaflet edges. Commissurotomy and resection of myxomatous tissue were performed. Their postoperation courses were uneventful and they have been free from medication at present. These results suggest that aortic commissurotomy and resection of myxomatous tissue under direct vision may be preferable for critical aortic stenosis with dysplastic aortic valve.