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Abstract: Despite continuous efforts to improve robustness of cardiac valve implants, neither bioprosthetic, nor mechanical valves fulfill both hemodynamic and durability requirements. This study presents novel flexible leaflet designs, focusing on polymeric materials with proven hemocompatibility, such as PEEK, of much higher stiffness than native tissue, aiming on optimal valve implants. A biomimetic valve with a single-curvature belly-curve serves as referencefor the new design variants with a double-curvature belly-curve with varying radii. Soft (13.2 MPa), as well as stiff (2.4 GPa) leaflet materials, and different thicknesses are studied by means of lean simulations, and in-vitro experiments under physiologic hemodynamic conditions. The performance is assessed by opening pressure and orifice area. The latter is determined by a newly developed automatized image processing tool. Experimental trends are in agreement with simulations and demonstrate that a buckling inspired, double-curvature leaflet design, significantly enhances tri-leaflet valves’ opening behavior, particularly advantageous for stiffer leaflet materials. Best performing variant shows an opening pressure improvement in the range of 47% and 44% based on simulations and experiments, respectively, compared to reference, while achieved mean pressure differential is directly comparable to state-of-art bioprosthetic valves. The orifice area is slightly reduced for new variants, yet still in satisfying range.