In order to investigate the role of heavy nuclei in the heavy water cluster impact d+d fusion, we have undertaken a series of d+d fusion experiments using atomic and molecular heavy ions (C, O, Ne, Ar, Kr, and Xe) on the deuterated solid targets in the energy range of 0.4–4 MeV. The observed excitation functions of 3 MeV proton yields are well accounted for in terms of the two step knock‐on cascade model. No distinct differences were observed in d+d fusion rate even when the number of atoms in the oxygen molecule (O+, O2+and O3+) were changed. Extending the calculation of the excitation function of the atomic oxygen impact fusion rate up to the extremely low incident energies (∼keV), it has been found that the estimated proton yields are much smaller than the heavy water cluster impact fusion by 10 orders of magnitude. This indicates that the recent observation of strong enhancement of cluster impact d+d fusion from Brookhaven cannot be explained by the sum of usual elementary processes but must be due to some kind of non‐linear effect.