Background: We hypothesized that an ideal heart valve replacement would be acellular valve root scaffolds seeded with autologous stem cells. To test this hypothesis, we prepared porcine acellular pulmonary valves, seeded them with autologous adipose derived stem cells (ADSCs) and implanted them in sheep and compared them to acellular valves. Methods: Fresh porcine pulmonary valve roots were decellularized with detergents and enzymes. ADSCs were isolated from subdermal fat and injected within the acellular cusps. Valves were then implanted in an extra-anatomic pulmonary position as RV to PA shunts: Group A (n=6) consisted of acellular valves and Group B (n=6) of autologous stem cell-seeded acellular xenografts. Sheep were followed up for 6 months by echocardiography and histologic analysis was performed on explanted valves. Results: Early evolution was favorable for both groups. All Group A animals had physiologic growth without any signs of heart failure and leaflets were found with preserved structure and mobility, lacking signs of thrombi, inflammation or calcification. Group B sheep however expressed signs of right ventricle failure starting at one month, accompanied by progressive regurgitation and right ventricle dilatation, and the leaflets were found covered with host tissue. No cells were found in any Group A or B explants. Conclusions: Acellular stabilized xenogeneic pulmonary valves are reliable, stable, non-immunogenic, non-thrombogenic and non-calcifying scaffolds with excellent hemodynamics. Seeding these scaffolds with autologous ADSCs was not conducive to tissue regeneration. Studies aimed at understanding these novel observations and further harnessing the potential of stem cells are ongoing.