A mathematical model of the high-latitude ionosphere, developed earlier in the Polar Geophysical Institute, is utilized to calculate three-dimensional distributions of ionospheric parameters, modified by the action of the ionospheric heater. The model takes into account the convection of the ionospheric plasma, strong magnetization of the plasma at F-layer altitudes, and geomagnetic field declination. The calculations were made for two cases. Firstly, we simulated the distributions of the ionospheric parameters under natural conditions without a powerful high-frequency wave effect. Secondly, the distributions of the ionospheric parameters were calculated on condition that an ionospheric heater, situated at the point with geographic coordinates of the HF heating facility near Tromso, Scandinavia, has been operated, with the ionospheric heater being located on the night side of the Earth. The results of the numerical simulation indicate that artificial heating of the ionosphere by powerful high-frequency waves ought to influence noticeably on the spatial structure of the nighttime high-latitude F-region ionosphere in the vicinity of the ionospheric heater.