The formation of palladium deuteride during the electrolysis of heavy water is analyzed. This process is accompanied by thermal effects, such as local overheating, which can induce restructuring of the electrodes. The overheating depends on the size of the palladium-deuterium (Pd-D) clusters and the time scale for heat conduction. With the radius of the octahedral site occupied by deuterium in the Pd-D face-centered-cubic (fcc) lattice being similar or greater than the penetration depth of the temperature field for a single reaction of palladium with deuterium, Ruckenstein and Petty's equation has been applied in the calculation of the local overheating. A value of ∼2350°C for the maximum average temperature rise has been calculated for the Pd-D cluster formation. Similar calculations for the TiD2 fcc structure show that overheating probably depends also on the kinetics of D2 absorption. The presence of these phenomena may play some role in the reproducibility of cold fusion experiments.