The device has a delivering unit delivering electrical stimulation pulses of low energy to an electrode implanted in a heart chamber of a patient. A collecting unit collects electrical activity of the chamber, and comprises a producing unit for producing two distinct temporal components from two distinct electrogram intracardiac electrogram (EGM) signals of the chamber. An analysis unit performs a bi-dimensional analysis, delivers a descriptor parameter of two-dimensional non-temporal characteristic, and determines a presence or a loss of a capture based on the parameter.