Abstract: Cardiovascular malfunction is corrected by implantation through open-heart surgery of a prosthetic valve assembly in which a specially formed valve retainer ring, designed to be secured within a blood vessel by means of sutures, supports a plurality of valve flaps in uniquely hinged relationship. The hinged valve flaps are arranged to normally occur in a closed position in which adjacent flap edges, when in abutting relation to one another, limit hinging movement in one direction. The valve flaps are designed to closely resemble valve flaps in a human heart with hinged mountings devised to insure pronounced longevity being provided. Each valve flap, in response to systolic pressure, is free to move away from the normally closed position described. There is thus produced a central passageway through which fluid may flow in a substantial linear path of travel with little, if any, turbulence or traumatic effects being induced.