A heat-generating element includes at least one PTC heating element and an insulating housing enclosing the PTC heating element, as well as electric conductors whose inner surfaces are in contact with opposed sides of the PTC heating element. The respective outer surfaces of the electric conductors are covered by an insulating layer comprising at least two interconnected plastic sheets and fixedly connected to the housing. In another aspect, a heating device includes a plurality of heat-generating elements can comprise at least one PTC element and electric conductors that contact opposed lateral surfaces of the PTC element, and heat-emitting elements arranged in parallel layers in contact with opposed sides of the heat-generating element. The heating device has heat-emitting elements which are in contact with opposed sides of the heat-generating element via an interposed insulating layer comprising at least two interconnected plastic sheets.