A 12-year-old boy with complex cyanotic congenital heart disease with single-ventricle physiology was planned for univentricular repair. Aortopulmonary collateral occlusion using thrombotic embolization coils was planned, but during the procedure, there was perforation of an aortopulmonary collateral arising from the descending thoracic aorta. The teaching point from this case is that all aortopulmonary collaterals do not necessarily need to be occluded; when occlusion is performed, coils must be appropriately sized.
Keywords: aortopulmonary collaterals; coil embolization; cyanotic congenital heart disease; perforation.