Introduc on: Transcatheter valves manufactured using biological  ssue, as the essen al structural component, can be induced to: mechanical degrada on a er crimping and early calcifi ca on in pediatric pa ents. Objec ves: Manufacture and successful tests of one expandable polyurethane stent valve, may reduce the repeated opera ons of valve replacement, during the growing children. Material / Methods: I)Physical tes ng: Prostheses were submi ed to universal tes ng in machine EMIC and a computer with Tesc so ware, able to generate graphs of force versus deforma on (stretching). II)Hydrodynamic tes ng: Prostheses with diameters from 12 to 22 mm, were submi ed to pulsa le physiological fl ow and stress condi ons. III)Experimental implants in sheep: Ten sheep was submi ed to prosthesis implant, by trans catheter technique in pulmonary posi on. In Group A: Four sheep w/ <20 kg, the stent was expanded up to 18mm and in Group B: Six sheep w/ > 20 kg, expanded up to 22mm. Results: Physical and Hydrodynamic tes ng of Polyurethane strip removal of stent valve, before and a er undergoing to 30 minutes crimping, showed preserva on of proper es of resistance and elas city elonga on. In vitro durability was proven for >15 years. Eight sheep, were submited to 3D echo study, performed in the 6th month of f.-up,  showed:  there was no signifi cant transvalvular gradients and trivial regurgita on in 3 cases. Histologic, radiologic and electron microscopic study of the fi rst prosthesis shows: integrity of structure and free of calcifi ca on. Seven survival sheep are well, a er 24th months of follow-up.  Conclusion: Expandable polyurethane stent valve, with special design for implant and expansion in growing children, has experimental sa sfactory  hemodynamic performance and durability in vitro and in vivo tests. Calcifi ca on and structural changes were not observed. In the next step, clinical studies are be planned.