Abstract: The invention relates to a method and apparatus for determining the magnitude of heart-related parameters in a patient. In accordance with the invention, blood volume variation of a peripheral part of the body of a patient, which variation is cyclic in nature, is detected to provide a signal representative of the blood volume. The maximum amplitude, minimum amplitude of the signal at maximum slope, the time interval between the maximum and minimum amplitudes and the instantaneous cyclic repetition rate (period) of the signal are measured, and the parameters are calculated in accordance with appropriate formulae.