Baloon dilation is disappointing in maintaining patency of the arterial duct. In neonatal lambs, stent implantation in the arterial duct results in significantly larger ducts with greater pulmonary blood flow than balloon dilation. Little is known, however, about the duration of duct patency after stent implantation. The outcome of slent implantation into the arterial duct in 12 lambs was observed over a period of 1 to 24 months. Stents (Wallstent in 9, Tower stent in 3) were implanted after recanalizing the occuladed duct at 2 to 7 days of age. Heparin was given only during the procedure, but no further anticoagulants were ued. Anglographic or postmortem evaluations were made at 1, 1.5, 2, 3, 4, 6, 12, 16, and 21 months in a subgroup of 9 lambs who did not undergo reinterventions. The duct was patent in all these except for one studied at 16 months. Neointima initially developed in the center of the stent before extending toward the orifices, eventually gurying the metals strands in contact with the wall. From 4 to 6 months onward stenoses were present inside some of the stents. When the stent did not protrude into the aorta, neointima extended over the duct orifice. Metals strands that were not in contact with the duct all were incompletely covered with endothelial cells, platelets, and fibrin strands, but no thrombi were noted. Late balloon dilation of the stented duct was performed in two lambs increasing the pulmonary artery blood flow. In one lamb the neointimal lining was successfully removed at 14 months with an atherectomy catheter. Stent implantation into the arterial duct can maintain patency up to 21 months and could be considered as an alternative to neonatal systemic to pulmonary artery shunt operations. Neointimal proliferation and stenosis formation, however, is a major limitation that may eventually lead to a reduction in the pulmonary artery blood flow.