Abstract: An electric resistance heating element preferably of cylindrical or prismatic shape to be inserted into a test tube, a cartridge or in another cavity has one or more conductors connected to the supply system by the use of one or more electrodes. The conductors are made of a conductive composite material of a polymeric matrix with resistive function which are formulated at such ratio and materials as to achieve an electric resistance with high positive temperature coefficient (PTC) at the operation temperatures. The electrodes may be made of metallic materials. At least a core is made of insulating material, onto which the conductors with resistive function (PTC) and the electrodes are applied.