A valve prosthesis device suitable for implantation in body ducts, the device comprising an expandable support frame adapted to be initially crimped in a narrow configuration suitable for catheterization through the body duct to a target location and configured to be expanded to an expanded configuration in the target location, the support frame being provided with a plurality of longitudinally rigid support beams of fixed length； and a valve assembly comprising a flexible conduit having an inlet and an outlet, made of pliant material attached to the support beams providing collapsible slack portions of the conduit at the outlet, whereby when flow is allowed to pass through the valve prosthesis device from the inlet to the outlet the valve assembly is kept in an open position, whereas a reverse flow is prevented as the collapsible slack portions of the valve assembly collapse inwardly providing blockage to the reverse flow, characterized in that the support beams are provided with bores, the valve assembly is stitched to the support beams with thread or fiber through the bores and the outlet is tapered with respect to the inlet and the support frame at the outlet is wider in diameter than the pliant material forming the outlet.
