It is well accepted that Atrioventricular nodal re-entrant tachycardia (AVNRT) involves only a portion of the atria, while most of the atria, HIS bundle, and ventricle are not part of the re-entrant circuit. However, the exact nature of the circuit and the role of the upper and lower common pathways in AVNRT are not well defined. This study presents a case where re-entrant tachycardia exhibits spontaneous variability in intracardiac intervals. Electrophysiological manoeuvres elicit different responses due to the bystander pathway. The electrophysiological basis of these findings and their clinical implications are discussed.