A leadless implantable medical device comprises a first electrode configured to deliver electrical pacing energy, a second electrode configured to sense intrinsic electrical cardiac activity, and a third electrode configurable to both deliver electrical pacing energy and sense intrinsic electrical cardiac activity. The first and third electrodes are used for delivering electrical pacing energy and the second and third electrodes are used to sense intrinsic electrical cardiac activity. None of the first, second and third electrodes are incorporated into a lead.