The late appearance of pulmonary arteriovenous malformations after operations for complex congenital cardiac conditions may be explained in many ways. The necessity of hepatic blood flow to the lungs is now generally accepted for carrying some labile substance that is secreted by the liver and that has not yet been identified. Rerouting of hepatic blood to the lungs in cardiac patients can be accomplished with different methods, most of which are predisposed to thrombosis because of the slow flow in the tunnel. My colleagues and I describe a case of partial diversion of hepatic blood into the pulmonary circulation and suggest a strategy to decrease the likelihood of conduit thrombosis and to treat pulmonary arteriovenous malformations.