The postoperative course of a 15-month-old girl who underwent a bilateral bidirectional cavopulmonary connection was complicated by a left chylothorax and left hemidiaphragm paralysis. Two-dimensional and Doppler echocardiography revealed complete flow reversal in the left pulmonary artery. This flow abnormality was confirmed by angiography. Multiple aortopulmonary collaterals had also developed and were coil embolized at the time of catheterization. Coil embolization of the collaterals, combined with relief of the chylothorax and diaphragmatic plication, reestablished forward flow in the left pulmonary artery.