There is provided a device (100) and method for determining a total probability (Ptot) of Return of Spontaneous Circulation (ROSC) during an associated CPR procedure, which is being performed on an associated patient, comprising an input for receiving a set of photoplethysmograpy data (328, 330) having been obtained from the associated patient during the CPR procedure, and a processor (112) being arranged for carrying out one or more processes according to one or more predeterminedalgorithms (321, 322, 323, 324) so as to calculate the total probability (Ptot) of ROSC based on the one or more parameters, wherein the one or more processes are each, and/or in combination, being arranged for overcoming challenges derived from the CPR process, such as arbitrary signals not related to return of spontaneous circulation. In embodiments, the device and method relies on a plurality of processes in determining the total probability of ROSC.