A newborn infant with tetralogy of Fallot and presumed agenesis of the ductus arteriosus presented without the expected associated pulmonic regurgitation and aneurysmal pulmonary arteries. The presumption of agenesis of the ductus arteriosus was made because there was no reduction in cyanosis following prostaglandin E1 treatment and no remnant of ductus arteriosus could be demonstrated by angiography at 19 h of age. The fetal hemodynamics inferred in this infant are discussed with reference to the absence of aneurysmal pulmonary arteries. Closed transventricular pulmonary valvulotomy is recommended as emergency palliation for symptomatic newborns with this variant of tetralogy of Fallot because further reduction of pulmonary vascular bed, even temporarily, as in unilateral pulmonary artery cross-clamping for systemic-pulmonary anastomosis, may not be tolerated without the use of cardiopulmonary bypass.