Major aortopulmonary collateral arteries in association with atrioventricular septal defect with balanced ventricles and trisomy 21.

A major aortopulmonary collateral artery is a rare and easily missed diagnosis that is usually associated with Tetralogy of Fallot or pulmonary atresia. We present two cases of major aortopulmonary collaterals associated with trisomy 21 and atrioventricular septal defect with balanced ventricles in which the diagnosis went undetected until after initial cardiac repair.