A heat exchanger, comprising - at least one PTC element, - at least two conductors connected to the at least one PTC element in an electrically conductive manner in order to direct electrical current through the at least one PTC element and thereby heat the PTC element and - at least one thermally conductive element for transferring heat from the at least one PTC element to a fluid to be heated and - at least one means for connecting the at least one PTC element, the at least two conductors and the at least one thermally conductive element to one another, wherein at least one thermally conductive element is electrically insulated from at least one conductor by means of at least one first electrical insulating element, characterised in that the at least one first electrical insulating element is arranged between at least one conductor and at least one thermally conductive element and comprises a plate or coating made of ceramic or a film or coating made of plastic or a plate or coating made of mineral, and wherein at least one second electrical insulating element which electrically insulates the at least one PTC element and the at least one conductor is provided and the at least one first electrical insulating element consists of another material than the at least one second electrical insulating element and wherein the at least one second electrical insulating element is a curable or cured fluid or gel and the at least one second electrical insulating element electrically insulates the at least one PTC element and the at least one conductor in the areas in which the at least one PTC element or the at least one conductor are not in contact with or connected to the at least one PTC element or the at least one conductor or the at least one thermally conductive element or the at least one first electrical insulating element and covers a surface thereof. - at least one PTC element, - at least two conductors connected to the at least one PTC element in an electrically conductive manner in order to direct electrical current through the at least one PTC element and thereby heat the PTC element and - at least one thermally conductive element for transferring heat from the at least one PTC element to a fluid to be heated and - at least one means for connecting the at least one PTC element, the at least two conductors and the at least one thermally conductive element to one another, wherein at least one thermally conductive element is electrically insulated from at least one conductor by means of at least one first electrical insulating element, characterised in that the at least one first electrical insulating element is arranged between at least one conductor and at least one thermally conductive element and comprises a plate or coating made of ceramic or a film or coating made of plastic or a plate or coating made of mineral, and wherein at least one second electrical insulating element which electrically insulates the at least one PTC element and the at least one conductor is provided and the at least one first electrical insulating element consists of another material than the at least one second electrical insulating element and wherein the at least one second electrical insulating element is a curable or cured fluid or gel and the at least one second electrical insulating element electrically insulates the at least one PTC element and the at least one conductor in the areas in which the at least one PTC element or the at least one conductor are not in contact with or connected to the at least one PTC element or the at least one conductor or the at least one thermally conductive element or the at least one first electrical insulating element and covers a surface thereof.