As there is currently no suitable valved pulmonary conduit for small children, porcine conduits treated by the L-Hydro process were implanted into 9 newborn lambs to investigate growth potential. Of the 8 survivors, 7 were kept alive for 12 months after implantation. The diameter of the conduit and gradient across the valve were evaluated at surgery and at 3 and 9 months postoperatively using bidirectional echocardiographic and angiographic methods. After sacrifice, histological and radiological analyses were performed. The mean weight of the animals was 4.2 +/- 1.1 kg at implantation and 43.1 +/- 6.2 kg at sacrifice. There was a significant increase in mean valve area from 139.9 +/- 18.0 mm2 at implantation to 443.5 +/- 89.2 mm2 at 12 months. Pre-sacrifice angiography showed no transvalvular gradient, and radiographic analysis did not reveal significant conduit wall or leaflet calcification in any of the animals. Histological examination of the grafts demonstrated total integration, with native-like intact valve leaflets. Thus functional evaluation, echocardiography, and histology demonstrated growth of the grafts with completely endothelialized and apparently normal pulmonary valve leaflets without calcification.