ABSTRACTFetal echocardiography has yet to have an impact on the treatment of congenital heart disease. Critical aortic valve stenosis was diagnosed by echocardiography before birth in a 35 week gestation fetus. The risks to the fetus and mother associated with prolonged rupture of membranes prompted their transport to a hospital with cardiac surgical and high-risk perinatal facilities. Prenatal and postnatal echocardiographic findings agreed regarding the diagnostic criteria for critical aortic stenosis and primary forms of cardiomyopathy were excluded. Results of fetal Doppler examination were consistent with valvular aortic stenosis and excluded mitral regurgitation. Determination of the left ventricular size excluded ventricular hypoplasia. The infant was delivered by cesarean section and underwent successful emergency aortic valvotomy at 12 hr of age. Fetal echocardiography, in combination with a multidisciplinary postnatal approach, can be used in the successful treatment of a severe form of congenital heart disease.