An implantable medical device and a method for operating such a device to provide cardiac pacing to the heart of a patient for pacing hearts of patients suffering from periodical or intermittent atrio-ventricular blocks, for example, AV block or HIS block. A control circuit operates the device in a DDI-II mode, the DDI-II mode being an operation mode with an atrial inhibited pacing and a DDI-II mode ventricular pacing rate being lower than a predetermined base rate of a pulse circuit of the device, during periods with atrio-ventricular conduction conditions. If a block in atrio-ventricular conduction is detected and at least one first switching criterion is satisfied, the control circuit causes a switching circuit to switch from the DDI-II mode to the DDI mode and, if a block in atrio-ventricular conduction is detected and at least one second switching criterion is satisfied, the control circuit causes the switching circuit to switch from the DDI mode to the DDD mode. The control circuit is adapted to control the switching circuit to switch back to the DDI-II mode at satisfaction of a reinitiating criterion.