At auroral latitudes the electron heat flow resulting from solar EUV heating, as well as magnetospheric energy input, are important parameters which dirve the thermal electron structure of the upper ionosphere. A method is presented which allows a determination from EISCAT-VHF observations of the heat flow at two altitudes, typical of the collision-dominated F2 region and of the topside ionosphere. EISCAT midwinter and near-summer observations are used to illustrate the method: diurnal and seasonal variations of solar origin are evidenced, with peculiar enhancements at sunrise and sunset that are interpreted as a delay between the F2 level and topside terminator passage. Perturbations of magnetospheric origin are then discussed. One of them is characteristic of low-altitude energy inputs. Others correspond to high-altitude energy inputs through heat flow variations and are interpreted as upward currents of the order of 14 &mgr;A m-2. ¿ American Geophysical Union 1994