The invention relates to a method and a heating device (1c) for inductively heating a stator (2) or armature (3) of an electric machine, in particular before and during trickle impregnation thereof. In addition, the invention relates to an impregnating device (50) in which this heating device (1c) is integrated. According to the invention, it is provided that the heating takes place inductively by electromagnetic fields of different frequencies. For this purpose, it is provided in the case of the heating device (1c) that it has at least one electromagnetic inductor (18, 21, 24) which is disposed coaxially or axially parallel with respect to the longitudinal axis (7) of the stator (2) or armature (3) and which inductively heats said stator or armature, and that the at least one inductor (18, 21, 24) is designed to generate at least two electromagnetic fields of different frequencies.