The cooling of a heated electron gas by electron impact excitation of CO2 is believed to be an important process in the neutral atmospheres of Mars and Venus. Electron energy loss rates are calculated for a variety of excitation processes as a function of electron temperature at a CO2 gas temperature 0f 200 K. Vibrational excitation is found to be the most efficient cooling mechanism for the range of electron temperatures studied. The contributions of various vibrational energy loss processes to electron cooling are discussed.