a catheter including a support suitable for insertion into a body organ , a transducer carried by the support , the transducer including a flexible piezoelectric polymeric membrane , and a pair of surface electrodes mounted on the membrane , the support including a rigid portion defining a flexure cavity inside the catheter , the membrane being mounted on the rigid support portion to permit free flexing of the membrane into and out of the cavity , one surface of the membrane communicating with the cavity , the other surface of the membrane being exposed to the exterior of the catheter to receive and flex in response to pressure variations in the organ , and an electrical cable for transmitting from the electrodes to external circuitry electrical signals produced by said flexure .