Although the etiology of pulmonary fistulas in congenital heart disease remains unknown, several hemodynamic factors are thought to play a role. Recently it was postulated that hepatic venous effluent might protect the pulmonary bed from development of pulmonary fistulas. However, there are no experimental data supporting this hypothesis. Here, we present the cases of 2 patients in whom pulmonary fistulas developed after unintentional surgical exclusion of the hepatic venous flow from the pulmonary circulation. In both patients, symptoms resolved after rerouting of the hepatic venous blood to the lungs.