A physiological pressure transducer assembly mounted on a transvenously-insertable guide wire is disclosed. The multiple coils of the guide wire define an elongated tubular passage within which fiber optic leads are contained for the transmission of light signals to a pressure transducer. A window or aperture is cut along a restricted portion of the length of the guide wire coil to provide a pressure-sensing aperture over which an elastic, pressure-sensitive membrane is positioned. The coils of the guide wire adjacent to the sensing aperture are joined together for increased rigidity along the length of the pressure transducer assembly, as by soldering or brazing. A separate, cylindrical housing, preferably of molded plastic, is wholly contained within the reinforced length of the guide wire. The proximal end portions of fiber optic sending and receiving leads or paths are received and contained within the housing in a predetermined arrangement and geometry defining a light-transmitting gap. Light transmission across the gap is controllably attenuated by deflection of the pressure-responsive membrane in response to pressure changes within a person's body, and the attenuated light signals are transmitted to an external control unit as indicative of pressure changes. A reflector positioned on an end cap closing the proximal end of the elongated guide wire is utilized to reflect signals from the signal transmitting, fiber optic lead or path to the proximal end portion of a return signal, fiber optic lead or path.