A device that can be temporarily introduced in a body or permanently implanted in a body comprising at least one elongated electric function conductor for transmitting treatment signals or diagnostic signals, or both, and further comprising a connector, which is connected to the function conductor and disposed on a proximal end of the function conductor, for connecting the device to a further device. Characteristic impedance is present between the function conductor and at least one further conductor. A transition region from the function conductor to the connector is designed such that a characteristic impedance between the function conductor and the further conductor in the transition region is designed to be between the corresponding characteristic impedance of the device in a line section distal of the transition region and the characteristic impedance present proximal of the transition region when the connector is connected to a further device.