Stimulation system for indicating stimulation signals to a user, provided with at least one heart beat sensor for converting measured heart beats into a signal, a processing circuit configured to process the measured heart beat signals, a user interface configured to indicate stimulation signals to a user, wherein the processing circuit is configured to calculate intervals between the detected heart beats and register a predetermined number of successive intervals, predict a time interval between a detected heart beat and a predicted future heart beat based on the registered intervals, and instruct the user interface to indicate a stimulation signal to a user non-simultaneously with the predicted heart beat at the end of the predicted time interval so as to change the heart rate and/or heart coherence of the user.