System for filtering cardiac signals, the system comprising: - a plurality of cardiac terminals (10a-d) adapted to collect cardiac electrophysiological potentials from a plurality of cardiac electrodes (1a-d) placed at respective cardiac locations in or on an individual; - one or more indifferent terminal(s) adapted to collect one or more indifferent electrophysiological potentials from one or more indifferent electrodes placed in or on the individual; - a differential amplifier stage adapted to amplify the electrophysiological potentials collected from the cardiac and indifferent terminals with respect to a signal reference to obtain respective cardiac and indifferent signals; and - a processor device adapted to process one or more input signals which are based on the cardiac and/or indifferent signals, wherein said processing comprises running an adaptive filter algorithm on one or more intermediate signals based on the input signals, said adaptive filter algorithm being arranged to calculate one or more estimated noise component(s) of said one or more intermediate signals and being arranged to subtract said one or more estimated noise component(s) respectively from said one or more intermediate signals; wherein the one or more estimated noise components of said adaptive filter algorithm are estimated as one or more sinusoidal waves; whereby - the processor is adapted to calculate an average of more than one of the one or more cardiac signal(s) and/or the one or more indifferent signal(s), wherein said calculated average is used to generate an estimate of a common mode signal and to provide an estimate of an instantaneous frequency of the noise component based on the estimated common mode signal. - a plurality of cardiac terminals (10a-d) adapted to collect cardiac electrophysiological potentials from a plurality of cardiac electrodes (1a-d) placed at respective cardiac locations in or on an individual; - one or more indifferent terminal(s) adapted to collect one or more indifferent electrophysiological potentials from one or more indifferent electrodes placed in or on the individual; - a differential amplifier stage adapted to amplify the electrophysiological potentials collected from the cardiac and indifferent terminals with respect to a signal reference to obtain respective cardiac and indifferent signals; and - a processor device adapted to process one or more input signals which are based on the cardiac and/or indifferent signals, wherein said processing comprises running an adaptive filter algorithm on one or more intermediate signals based on the input signals, said adaptive filter algorithm being arranged to calculate one or more estimated noise component(s) of said one or more intermediate signals and being arranged to subtract said one or more estimated noise component(s) respectively from said one or more intermediate signals; wherein the one or more estimated noise components of said adaptive filter algorithm are estimated as one or more sinusoidal waves; whereby - the processor is adapted to calculate an average of more than one of the one or more cardiac signal(s) and/or the one or more indifferent signal(s), wherein said calculated average is used to generate an estimate of a common mode signal and to provide an estimate of an instantaneous frequency of the noise component based on the estimated common mode signal.