During fetal development, little blood flows through the lungs due to high pulmonary vascular resistance. After birth, pulmonary vascular resistance is initially elevated and then decreases over the first few days of life. In normal infants the ductus arteriosus is not needed after birth and begins to functionally close during the first 24–72 hours after birth. It is anatomically closed between the third and fourth week of life. In infants with critical pulmonary valve stenosis, the amount of antegrade blood flow through the pulmonary valve to the pulmonary arteries is limited, and therefore the major source of source of pulmonary blood flow is provided via the ductus arteriosus. As it closes, if antegrade blood flow through the critically stenosed pulmonic valve is not sufficient infants become hypoxemic and may require institution of prostaglandin E1 to maintain ductal flow. Balloon pulmonary valvuloplasty in the cardiac catheterization laboratory is the treatment of choice for the typical dome-shaped valve characteristically seen in pulmonary stenosis. This chapter describes the perioperative considerations and management of an infant with critical pulmonary stenosis undergoing balloon valvuloplasty in the catheterization laboratory.