An implantable cardiac monitor upgradeable to an implantable pacemaker or an implantable cardiac resynchronization device allows the use of a single implantable medical device for monitoring cardiac conditions and later, if needed, for cardiac pacing. The implantable medical device includes a circuit that can be configured, by programming through an external programmer, to either the implantable cardiac monitor or the implantable pacemaker. The implantable medical device is first configured to and used as the implantable cardiac monitor for acquisition of physiological data indicative of a need for a pacing therapy. If the pacing therapy is to follow, the implantable medical device is reconfigured from the implantable cardiac monitor to the implantable pacemaker, thus eliminating the need of using two implantable medical devices.