the invention relates to a heat exchanger , particularly for a heating or air conditioning unit of a motor vehicle , comprising several flat pipes which are arranged parallel to each other and are penetrated by a heat - transmitting medium . an electrically operated heating element which is mounted once the heat exchanger has been soldered is assigned to at least one part of the flat pipes as an additional heating device . said heating element is fixed to the heat exchanger by means of a holding element is mounted in front of the corresponding flat pipe and parallel thereto by means of the holding element which also runs parallel to the flat pipe .