The investigations of the heteronuclear 3d-4f spin systems are of current interest, since such compounds have relevance in materials science (molecule-based magnets, zeolite-like materials, etc.). Recently it has been shown that 3d-4f heteronuclear complexes can be used as tectons in constructing extended structures [1]. Of particular interest are Cu-Gd dimers because in the most of the previously studied systems the ferromagnetic interaction Cu(II)-Gd(III) was established. These conclusions were obtained on the base of magnetic susceptibility data. We present the EPR investigation of the ladder-type compound [{CuL}Gd(H2O)3{Fe(CN)6}] 4H2O built up of the Cu-Gd dimers connected by [Fe(CN)6]3- spacers. Compounds with different combinations of paramagnetic and diamagnetic centers (La3+, Co3+) are investigated also: [{CuL}Gd(H2O)3{Co(CN)6}]4H2O and [{CuL}La(H2O)3{Fe(CN)6}]4H2O. This enabled the investigation of exchange interactions in the fragments of this system and the analysis of the effectiveness of various interaction channels. Compounds consisting Cu-Gd dimer fragments which compose the chains were studied as well. It is the first example of a detailed investigation of the Cu(II)-Gd(III) system by EPR. The possibility to determine the character of the Cu-Gd exchange interaction by analyzing the temperature dependence of the fine structure of EPR spectra is discussed. Synthesis, crystal structure and magnetic properties of these compounds were reported earlier [2,3].