This study was undertaken to investigate the degeneration and calcification of valved bovine jugular vein segments for right ventricular outflow tract reconstruction in juvenile sheep. Seven valved bovine jugular vein conduits (Contegra model 220; VenPro Corporation, Irvine, Calif) and 3 control conduits (MH100; Medtronic, Inc, Minneapolis, Minn) were implanted in the pulmonary artery in young sheep. After 20 weeks the conduits were explanted and qualitatively analyzed by epicardial echocardiography, gross examination, x-ray analysis, light microscopy, and transmission electron microscopy. Calcification was determined quantitatively by flame atomic absorption spectrometry. Two Contegra conduits could not be analyzed because of endocarditis. All other Contegra conduits functioned well, with preserved structure and minimal calcification. The control MH100 conduits exhibited extensive fibrous sheathing, with calcification of the aortic wall portion and the commissural part of the Hancock valve. The Contegra conduit's performance was clearly superior to that of the control MH100 conduit when implanted in the pulmonary artery position in juvenile sheep for 5 months.