BACKGROUND Transcatheter aortic valve replacement (TAVR) has recently been shown to be equivalent to surgical aortic valve replacement (SAVR) in intermediate-risk patients. As TAVR expands towards the traditionally SAVR population, TAVR versus SAVR durability becomes increasingly important. While the durability of TAVR is unknown, valve design - particularly with regards to leaflet stress - impacts on valve durability. Although leaflet stress cannot be measured directly, it can be determined using finite element modeling, with such models requiring the mechanical properties of the leaflets. Balloon-expandable TAVR involves the use of bovine pericardial leaflets treated in the same manner as surgical bioprosthetic leaflets. The study aim was to determine the leaflet mechanical properties of Carpentier-Edwards bioprostheses for future TAVR and SAVR computational models. METHODS A total of 35 leaflets were excised from 12 Carpentier-Edwards Model 3000TFX Perimount Magna aortic bioprostheses (21 mm, 23 mm, and 25 mm) and subjected to displacement-controlled equibiaxial stretch testing. The stress-strain data acquired were fitted to a Fung constitutive model to describe the material properties in circumferential and radial directions. Leaflet stiffness was calculated at specified physiological stress, corresponding to zero pressure, systemic pressure, and between zero and systemic pressure. RESULTS The 21-mm bioprostheses had significantly thinner leaflets than the larger bioprostheses. A non-linear stress-strain relationship was observed in all leaflets along the circumferential and radial directions. No significant difference in leaflet stiffness at systemic pressure, or between zero and systemic pressure, was found among the three bioprosthesis sizes. However, the leaflets from the 23 mm bioprosthesis were significantly more compliant than those of the 21 mm and 25 mm bioprostheses at zero pressure in the circumferential direction. No differences were observed in leaflet stiffness in circumferential versus radial directions. CONCLUSIONS The bovine pericardial leaflets from Carpentier-Edwards Perimount Magna bioprostheses showed no differences in material properties among different valve sizes at systemic pressure. The thinner 21 mm leaflets did not show any corresponding differences in leaflet stiffness, which suggests that the thinner TAV leaflets may have a similar stiffness to their thicker SAV counterparts.