The invention regards an implantable heart monitoring device (10) comprising a sensing unit (58, 66), a signal quality analysis unit (96), and an evaluation unit (98). The sensing unit (58, 66) can be connected or is connected to at least one electrode (22, 24, 30, 32), which is configured for picking up electric potentials. The sensing unit (58, 66) is adapted to process electrical signals corresponding to said electric potentials, to detect signal components representing a myocardial contraction, and to generate sense signals comprising events (102, 104) corresponding to myocardial contractions. The signal quality analysis unit (96) is configured to determine whether a noise condition (NC) and/or a low signal indication is present for an event (102, 104) and to generate a noise condition and/or low signal indication signal. The evaluation unit (98) is connected or connectable to said sensing unit (58, 66) and said signal quality analysis unit (96) and configured to evaluate sense signals and noise condition and/or low signal indication signals. The evaluation unit (98) is further configured to treat a detected event (104) as non-valid if a noise condition (NC) and/or low signal indication signal is present for that event (104) and to use only intervals (106) defined by two consecutive events (102) which do not have a noise condition (NC) and/or a low signal indication to determine a rate of events of the sense signal.
