Guerra MC, et al. - Among patients having atrioventricular re-entrant tachycardia (AVNRT) or orthodromic atrioventricular tachycardia (AVRT), researchers assessed the incidence and mechanism of a single ventricular premature beat (VPB) on initiation and termination of tachycardia during programmed electrical stimulation (PES) of the heart. This study included 337 prospectively enrolled consecutive patients over 18 years old with an inducible sustained AVNRT or AVRT. Excluded cases were those with more than one tachyarrhythmia mechanism. A single VPB during sinus rhythm initiating supraventricular tachycardia (SVT) was an infrequent finding, which favored AVRT. It was a common finding in AVRT that a single VPB terminated SVT, however, this was seldom seen in AVNRT. When interpreting a noninvasive arrhythmia event recording, these revelations can be of help.