We analyse theoretical and by numerical simulations the relationship between a unipolar electrogram at an exploring site , the unipolar electrogram recorded at a permanentely depolarized site and a reference potential . For equal anisotropic ratio between the intra and extracellular media, when choosing the depolarized site as reference potential, the electrogram at the exploring site usually called unipolar monophasic action potential apart from scaling, coincides with transmembrane action potential at the exploring site. For general anisotropy others potential components must be added to the previous transmembrane action potential component and we compare the ideal monophasic action potential with the those simulated for general anisotropy.