NOVELTY - The flat element comprises a front side and a rear side, which has a heating layer and a contacting layer, where the heating layer consists of an intrinsically heatable self-adhesive mass (10), which is formed as a conductor heating itself during passing an electric current. The contacting layer is formed as a contacting element (20) expanded in a flat-shaped manner and broken by notches and has a first side surface and a second side surface. The contacting layer contacts with the heating layer over the first side surface and is electrically conductively connected with the heating layer.    USE - Flat element useful for heating an adhesion substrate (claimed) such as mirror with mirror holder, articles or chambers of electric heaters, in automobile industry for heating car seats, window panes and automotive exterior mirrors, as a mirror heater such as outdoor and indoor mirrors in a heated inner lining, for wipe water heating or freezing-security, for tank heating for diesel vehicles, for heating fuel lines, in a heater for defrosting systems, in steering wheel heater, for heating hot air or for preheating suction air such as combustion air, as a display window, windshield or bathroom mirrors, as anti-fog lamination for bathroom applications, as heatable tile adhesive film, for seating on bus stops, sports stadiums, restaurants and outdoors or for toilet seats, in heating covers or mats, in heating plates for foods and dishes, in belt heater for piping and boilers, for solar cells, as wall heater, floor heater, foldable tent heater, large radiant heater, saddle heater, greenhouse heater, convection heater and waterbed heaters, in heatable housing as thermobox for temperature control of the content or housing in the electronics sector, for motorcycles, for small-scale local heating directly on the plants such as root heating, as heater for functional clothing e.g. in motorcycle clothing and winter clothing, for heating and attaching a display system e.g. LCDs, organic light emitting diodes and electrophoretic displays, as freezing protection for displays in cameras or external displays or in alarms, in incubators, in medical therapy e.g. on the surface of a human or animal body in the heat therapy, for heating of external switches, and as a heat patch for transdermal and therapeutic systems for transdermal medication.    ADVANTAGE - The flat element prevents the transmission of electrically produced heat energy on the adhesion substrate, can be simply structured, has high flexibility, high heating functionality, high reliability, good mechanical properties, high strength and high rigidity, can be easily joined with the adhesion substrate without the risk of damaging the delicate structures such as electrically conductive structures, and is capable of rapidly heating the adhesion substrate.    DETAILED DESCRIPTION - The flat element comprises a front side and a rear side, which has a heating layer and a contacting layer, where the heating layer consists of an intrinsically heatable self-adhesive mass (10), which is formed as a conductor heating itself during passing an electric current. The contacting layer is formed as a contacting element (20) expanded in a flat-shaped manner and broken by notches and has a first side surface and a second side surface. The contacting layer contacts with the heating layer over the first side surface and is electrically conductively connected with the heating layer. The second side surface of the contacting layer forms the front side of the flat element. The notches are continuously formed in the contacting element over the thickness of the contacting element and are present in the area of the second side surface in an adhesive-free manner. The intrinsically heatable self-adhesive mass is a positive temperature coefficient (PTC) thermistor. The first side surface of the contacting layer is partially embedded into the intrinsically heatable self-adhesive mass, and lies on a side surface of the intrinsically heatable self-adhesive mass in a flat manner. The thickness of the contacting element is less than 20 mu m. The notches form more than 50% of the surface of the first side surface of the contacting layer or more than 75% of the first side surface of the contacting layer. The broken contacting element has web-shaped areas, which have a width of highly 5 mm or less than 1 mm and are present in a branched comb structure or finger structure. The intrinsically heatable self-adhesive mass comprises an electrically conducting filler material, which comprises graphite, carbon nanoparticles and conductive soot. An INDEPENDENT CLAIM is included for a method for joining a flat element with an adhesion substrate.    DESCRIPTION OF DRAWING(S) - The diagram shows a schematic longitudinal view of a flat element.    Self-adhesive mass (1)    Contacting element (20)    Adhesion substrate. (30)