Abstract: Apparatus for measuring the variability of cardiovascular parameters, having a photoplethysmographic (PPG) probe, including a modulated first light source and a photodetector, a demodulator connected to the photodetector for demodulating PPG signals detected by the photodetector, an analog to digital converter for digitizing the demodulated signals, and a processor for repeatedly analysing the PPG signals for a predetermined number of times. A method for measuring the variability of cardovascular parameters.