Late cardiac tamponade is an infrequent complication of pediatric cardiac surgery. It is usually accompanied by the postcardiotomy syndrome and can occur after open or closed cardiac operations. It may occur despite treatment of the postcardiotomy syndrome. Five children were treated for late cardiac tamponade. All were treated initially with anti-inflammatory drugs; four also required pericardiocentesis, and two of these required subsequent creation of a pericardial window. One patient died due to delay in performing operative decompression. Late cardiac tamponade can be a lethal complication in children.