Introduction
During orthodromic reciprocating tachycardia (ORT), or atrioventricular reentrant tachycardia, functional bundle branch block (BBB) can be present when wavefront encroaches on the refractory period of His-Purkinje system. Ventriculo-atrial conduction time is shortened when bundle branch conduction is improved during ORT utilizing ipsilateral concealed accessory pathway (AP) [1-3]. However, this may exactly advance wavefront to the refractory period of the circuit components which results in tachycardia termination. Here we describe a group of patients sharing the phenomenon of ORTs relying on aberrant conduction based on various mechanisms.