Abstract: An improved valve prosthesis for causing nontraumatic unidirectional flow of a pulsatory fluid, such as blood, through a conduit, such as a blood vessel. The valve includes two flaps, made of a suitable flexible material, attached by the proximal ends to opposite sides of a covered annular mounting structure. A pair of magnetic members are connected to the distal ends of the flaps thereby to exert sufficient attractive force to hold the flaps together in a closed position to prevent fluid flow through the valve. The magnetically-closed flaps are forced to an open position by the pressure of the fluid flowing through the conduit. A decrease in fluid pressure in combination with the attractive force exerted by the magnetic members permits the smooth, nontraumatic closure of the valve flaps.