Abstract: An improved heart valve prosthesis (20) suited for replacement of any of the four valves in the heart. The invention includes a generally annular orifice ring (22) having a fluid flow bore with a smooth inner wall (26) through which blood flows, controlled by two pivoted leaflet occluders (40), supported at the downstream edge of the orifice ring.The occluders are supported at the outboard edges of the orifice ring, overlapping the fluid flow bore and generally about each other to seal backflow and regulate flow in one direction only. Occluder travel is limited by bending moment resistance of the occluder hinge and lateral blood flow. Occluder hinges are unloaded at a point between fully opened and fully closed.The bearing surfaces between the occluder means and the annular orifice are wide enough to allow the valve to be constructed from materials of different hardnesses.