An electronic instrument designed to test an implanted cardiac pacemaker, including the lead/tissue interface at the time of implantation, for invasive pacemaker evaluation and/or during electrophysiology (EP) diagnostic procedures. It has testing and recording capabilities to measure the minimum electrical stimulus needed to elicit ventricular contraction and the minimum intracardiac signal amplitude needed to inhibit the pacemaker (i.e., stimulation and sensing thresholds respectively). It typically includes measuring devices for the bioelectrical signals, a pulse generator, controllers, and the capability to test the characteristics and performance of the implanted pacemaker.