Cardiac/coronary catheter, comprises a fluid delivery conduit for connection, at a distal end of the conduit, to a patients circulatory system, pressuring monitoring means 238 for monitoring the blood pressure, said pressure monitoring means being in fluid communication with the system via the conduit, the apparatus includes compensation means 260 for use in compensating for, or reducing the effect of, the flow of fluid through the conduit on the output of the pressuring monitoring means. The apparatus may be used in fractional flow reserve (FFR) procedure. The compensation means may combine the outputs of the pressure monitoring means and another pressure sensor to give an output of the blood pressure. The compensation means may comprise a Wheatstone bridge. The pressure monitoring means may be a differential pressure sensor and may comprise a Venturi tube.
