Determining the presence and type of a probe associated with an active implantatable medical device, in particular a cardiac pacemaker and devices having similar pacemaker functionality. This device includes circuits for producing monopolar or bipolar stimulation pulses, selectively with or without disconnection of a connection (S1, S2) to a reference potential, and a circuit for sensing a pulse signal produced by the variation of potential induced on one and/or the other of terminals (RING, TIP) and/or on the metallic case (CASE) in response to an application of stimulation pulses. The device operates to analyze a characteristic of the shape (28), in particular the pulse width, and to deliver an indicator representative of the presence or the absence of a probe. The device also can selectively modify at least one operating parameter of the device according to the delivered indicator.