This report describes a case in which an implanted pacemaker programmed to perform noninvasive electrophysiology testing resulted in an unusual form of pacemaker mediated tachycardia. The method of chest wall stimulation was used by programming a unipolar, triggered pacing mode with a short refractory period. In the AAT mode, far-field R wave sensing occurred beyond the physiological atrial refractory period. The triggered atrial response resulted in a single chamber, pacemaker mediated tachycardia.