Abstract: An extracorporeal apparatus is provided for use with an implantable medical device and has a telemetry unit for receiving a telemetry signal transmitted from the implantable device. The extracorporeal apparatus further includes a transmission member disposed downstream of the telemetry receiver for compensating for the signal influence contained in the telemetry signal and effected by a first transmission member in the implantable device for the purpose of interference-free reproduction of a measuring signal received by way of the implantable device in the body, and/or for simulating the signal influence effected by a second transmission member in the implantable device for the purpose of external modelling of the dependency of the device behavior on the measuring signal.