A healthy full term infant is born with RV dominance. LV dominance with a trend toward RV dominance with increasing gestational age was found in preterm infants by EKG and echo criteria.

Congenital aortic stenosis accounts for about 5% of cardiac malformations recognized in childhood. It belongs to the category of acyanotic congenital heart disease. These lesions produce a load on the heart because of left ventricular outflow tract obstruction. Severe aortic stenosis in the newborn period (critical aortic stenosis) presents with signs of left sided heart failure (pulmonary edema, poor perfusion), right sided heart failure (hepatomegaly, peripheral edema) and may progress rapidly to total circulatory collapse. We present a case of an infant with critical aortic stenosis presenting with cyanosis, who was entirely dependent on ductal patency for systemic output. When oxygen was given, the ductus started to close, with a worsening of the left sided output and subsequent acidosis. With the right to left shunt across the ductus, the baby was cyanotic and dependent on prostaglandin to keep the ductus open. There was minimal flow across the aortic valve because of the stenosis and extremely poor left ventricular function prior to surgery. After relief of the aortic valvular obstruction, there was finally good antegrade flow across the aortic valve, terminating cyanosis.