1. A device for processing signals representative of a cardiac potential of depolarization of the myocardium for reconstruction of a surface electrocardiogram (ECG), comprising: a plurality of inputs, corresponding to a plurality of EGM signals from endocardial or epicardial electrogram (x 1 , x 2. .. x Q ) each acquired on a respective EGM derivation of a plurality of EGM derivations ( 10 ); at least one output delivering a reconstructed surface electrocardiogram ECG signal (yj), relative to an ECG ( 16 ) derivation; and a non-linear digital filter including a Volterra type filter (F 1 , F 2. .. F Q ) ( 12 , 14 , 12 ′, 12 ″, 14 , 12 , 52 ) with a transfer function that reconstructs said ECG signal derivation based on said plurality of inputs, said transfer function including a linear term (h 1 ) and at least one quadratic (h 2 ) and/or cubic (h 3 ) term(s).