Two infants with pulmonary atresia are presented, wherein a large, vertically oriented patent ductus arteriosus, acting as the only source of pulmonary blood supply, compressed the left bronchus, causing significant respiratory distress. Hyperinflation of the left lung was the clue to this circumstance. After bronchographic confirmation, surgical repair was accomplished by placement of aortopulmonary shunts and division of the patent ductus. Other causes of airway compression in congenital heart disease are briefly reviewed. The embryology of the ductus arteriosus is discussed, emphasizing its anatomic configuration and physiologic role in pulmonary atresia.