Abstract: A noninvasive arterial pressure monitor provides calibrated, continuous pressure waveform and beat-by-beat pressure values with no occlusion of an artery during an extended monitoring period. Noninvasive doppler sensors are secured over a major artery. Signals from the sensors are used to mathematically characterize the artery. The time-varying arterial resonant frequency is correlated to blood pressure throughout the cardiac cycle. Doppler sensors provide bi-directional flow velocity waveforms from which arterial resonant frequency may be calculated. A calibration cuff is used infrequently to calibrate the system to units of pressure.