Abstract: A system (1) for estimating the stroke volume and/or the cardiac output of a patient, comprises a processor device (12) constituted to receive a bio-impedance measurement signal (VC) relating to a bio-impedance measurement on the thorax (2) of a patient (2), process the bio-impedance measurement signal (VC) to extract a group of characteristic features from the bio-impedance measurement signal (DVC) and/or its derivative (DVC), and determine, using the group of extracted characteristic features, an output value indicative of the stroke volume and/or the cardiac output using at least one non-linear model (110, 111). The processor device (12) furthermore is constituted to process the bio-impedance measurement signal (VC) to compute at least one time-frequency distribution (TFD) based on the bio-impedance measurement signal (VC) and/or its derivative and to determine at least one characteristic feature of said group of characteristic features based on the at least one time-frequency distribution (TFD).