It is shown that Joule heating from electron collision damping of ac electric fields could be a significant source of energy for electrons in the Venus ionosphere if they occur naturally on a large scale. On the assumption that the fields are due to electromagnetic waves on a planetary scale, we calculate heating rates implied by observations on the day side and compare them with the profiles of photoelectron heating rates used by modelers. It is found that sufficient amplitudes have been measured on Pioneer Venus Orbiter in the frequency channels of 730 and 100 Hz to cause greater local electron heating rates than that due to photoelectrons, up to 3 orders of magnitude in some cases. Nightside heating rates at low altitudes for the 100-Hz signal would cause great heating of the ionosphere and thermosphère, airglow, and aurora. The difficulties produced by these findings would be relieved if the electric field disturbances were closely confined to the spacecraft or at least were much less than planetary in scale.