of the pacemaker does not include an atrial sensing state in its current programming this means that there are no transition rules that define how an atrial sensing state should be entered and exited nor does the pacemaker have an atrial channel refractory period timer which is needed in order not to misinterpret a ventricular depolarization or a pacing pulse as an atrial sense signal fig4 shows a state transition diagram of a pacemaker incorporating a testing system in accordance with the present invention a virtual sensing test state vs corresponding to the currently unprogrammed sensing channel i e the atrial channel in this case is added to the operation of the pacemaker where the pacemaker then operates as if programmed in a mode including that sensing state the virtual sensing test state includes a refractory period timer in its transition logic in order to properly interpret sensing signals the virtual testing state is thus transitioned to upon receipt of a sensing signal in the corresponding sensing channel and an amplitude value corresponding to the sense signal is stored in memory the term u201c virtual u201d in this context means that transition to the virtual sensing state results in no triggering or inhibition of pacing pulses as would be the case were the pacemaker simply programmed to operate with the atrial sensing channel active the transition rule of the virtual sensing test state is to return to the state from which the virtual state was entered in order to leave the programmed operation of the device undisturbed the testing states as described may be part of a.