The structural and energetic parameters of MU heterobimetallic dimers (M = Cr, Mo, W) have been computed using the complete active space self-consistent-field method followed by second-order perturbation theory. Our results show that the effective bond order (EBO) of the MoU dimer (5.5) is higher than that for the tungsten dimer (5.2), known to date as the molecule with the highest EBO. These heterodimers present also ultrashort bond distances and remarkably large dissociation energies, which make these molecules suitable and interesting potential candidates in synthetic bimetallic organometallic chemistry.