These tracings illustrate 2 causes of incessant PMT. On the first tracing, the PMT detection and termination algorithm was deprogrammed, thus explaining the persisting tachycardia. On the second tracing, the algorithm was reprogrammed, the device diagnoses the PMT, terminates it efficiently although the PMT immediately resumes. Indeed, atrial pacing occurs in the myocardial refractory period and is therefore ineffective and favors the occurrence of retrograde conduction. In this patient, it is necessary to diagnose the initial triggering mechanism of the PMT. Consideration should also be given to programming a PVARP that is longer than the retrograde conduction time, even if it appears relatively long (in the order of 400 ms) and that such prolongation may limit 1:1 tracking upon exertion. However, the exercise capacity of this 81-year-old patient is considerably reduced.