A system for online compensation and differentiation of blood-pressure pulse waves was developed which compensates for pressure-waveform distortion due to transmission, in fluid-filled catheters and provides outputs of pressure P, $$\dot P$$ , P/ $$\dot P$$ and $$\dot P$$ . The compensator can be tuned with the catheter in place by changing the natural frequency and damping ratio when these catheter parameters are altered by fibrin deposits, gas bubbles, and softening of the catheter wall. The compensator can be used with standard monitoring equipment and its output can be recorded or displayed on a cathode-ray-tube oscilloscope.