Disclosed is a heart monitor comprising an electric signal acquisition and processing stage connected or being connectable to two implantable electrodes (18,20,22,24) for picking up myocardial electric signals.said electric signal acquisition and processing stage comprising two signal processing channels, a first channel (66.1) comprising a first sampling stage (80) for sampling picked up myocardial electric signals with a first sampling rate, said first channel being adapted to process picked-up myocardial electric signal so as to generate an electrogram signal, and a second channel (66.2) comprising a high frequency sampling stage (82) for sampling at least portions of said picked-up myocardial electric signals with a second sampling rate, said second sampling rate being higher than said first sampling rate, a differential stage (84) adapted to generate a high frequency sampling output signal representing the difference between two consecutive high frequency sampled myocardial electric signal values and a comparator (86) that is adapted to compare said high frequency sampling output signal with a threshold and to generate a noise detection indicator whenever said threshold is exceeded.
