Objective To evaluate the early valve function following in situ transcatheter pulmonary valve implantation in sheep using a novel self-expanding ultramicroporous expanded polytetrafluoroethylene (ePTFE) pulmonary valve. Methods We designed a novel polymeric trileaflet transcatheter pulmonary valve with a self-expanding nitinol stent; the valve leaflet was made of 0.1-mm phosphorylcholine coated ultramicroporous ePTFE. Pulmonary valve stents were implanted in situ via the right ventricular apical approach in 7 healthy sheep, with an average weight of (27.2±1.2) kg. Right anterolateral thoracotomy was performed in the sheep under general anesthesia. Then the right ventricular apex was exposed, two purse-string sutures were made and the transcatheter valved stents were implanted in situ by puncturing the right ventricular apex. Angiography and hemodynamic measurements were obtained immediately after implantation to assess the valve function. Color Doppler echocardiography and hemodynamic measurements were used to assess the valve function 4 weeks after implantation. Results Implantation was successful in all the 7 sheep. Angiography immediately after implantation showed that all the prosthetic valves were in the orthotopic position and exhibited normal open and close function, without stenosis or insufficiency. One sheep died 16 days after implantation due to pulmonary infection with infective endocarditis. All the other sheep were in a good condition during a 4-week follow-up. Echocardiography 4 weeks later showed that all the prosthetic valves were at the orthotopic position and had normal function, with no significant thrombus or neoplasm. Echocardiography demonstrated no regurgitation in 4 sheep and trace regurgitation in 2 sheep. Hemodynamic findings showed that the peak-to-peak transvalvular pressure gradient of the polymeric valves was (6.0±2.2) mmHg (1 mmHg=0.133 kPa) immediately after operation and (9.5±2.7) mmHg at 4 weeks after operation, with the latter being significantly higher than that before implantation ([3.5±1.0] mmHg, P<0.05). Conclusion The right ventricular apical approach has a high successful rate for transcatheter pulmonary valve implantation, and the early function of the self-expanding ultramicroporous ePTFE pulmonary valved stents is satisfactory in sheep.