An implantable medical device having at least one elongated electrical function conductor that transmits therapeutic signals or diagnostic signals or both, and an electrode pole connected to the function conductor to deliver electrical current or field or sense electrical potentials in surrounding tissue during use, or both. Includes a sensing device which is connected to a field-generating electrode pole and potential-sensing electrode pole, and a reference pole, and which is designed to detect generated electrical potentials via the potential-sensing electrode pole in relation to the reference pole, and to generate an output signal which represents a detected electrical potential. Also has a control device connected to the sensing device to evaluate an output signal generated by the sensing device, and to control the medical device as a function of the potential detected by the sensing device.
