OBJECTIVE The concept of a lateral tunnel for the Fontan operation is now widely accepted. Most lateral tunnels are constructed intraatrially with the use of aortic crossclamping. Construction of extracardiac lateral tunnels with the use of homografts or other nonviable tubes eliminates aortic crossclamping but lacks growth potential in length or width. The native pericardium, which is "sealed" posteriorly along the pulmonary artery, atrium, and inferior vena cava, could be turned down onto the right atrium to form a viable extracardiac lateral tunnel. METHODS We designed and successfully constructed extracardiac lateral tunnels using viable autologous pericardium, pedicled on its lateral blood supply, in 19 patients aged 9 months to 5 years. All patients had a previous Glenn shunt; five patients had dextrocardia and a midline inferior vena cava. The patients' inferior vena cava-right atrial connection was opened transversely and the right atrial opening was sutured to its back wall, keeping the eustachian valve in the inferior vena cava. The underside of the right pulmonary artery was opened longitudinally; its inferior edge was sewn to the adjacent pericardial reflection. Any "pocket" or depressions in the posterior pericardium along the pulmonary veins were closed with running suture. Two incisions were made in the right pericardium down to the phrenic nerve parallel to the inferior vena caval and pulmonary arterial openings. This pedicled pericardium was trimmed and sewn as a roof to the upper edges of the inferior vena cava and pulmonary artery openings and then sewn longitudinally along the unopened right atrial wall, completing the viable extracardiac lateral tunnel. Although no fenestrations were used, these could be made during construction, or more significantly, owing to the lack of thick walled structures, in the catheterization laboratory in the postoperative period. RESULTS All 19 patients had respiratory/cardiac pulsations in the pulmonary arteries owing to the compressible lateral tunnel. At follow-up of up to 2 1/2 years, all tunnels are growing and no obstructions have occurred. CONCLUSIONS The viable autologous pericardial extracardiac lateral tunnel can be constructed without cardiac ischemia, can be fenestrated in the postoperative period, and forms a compressible, nonthrombogenic conduit capable of growth, which can be constructed early in infancy.