E stablishing the diagnosis of an atypical atrioventricular (AV) node-dependent long RP supraventricular tachycardia (SVT) can be difficult. Standard diagnostic criteria are lacking and often extrapolated from pacing maneuvers applied to the more common short RP SVT. Long RP SVTs involving concealed nodofascicular (NF) accessory pathways (AP) are particularly rare with descriptions limited to isolated case reports. [1][2][3][4] Prolonged conduction over the slow pathway (SP) of the AV node or a decremental AP after entrainment from the ventricle can produce A-A-V patterns that might be mistaken for atrial tachycardia (AT). 5 In addition, slow AP conduction after entrainment of an atypical orthodromic reciprocating tachycardia (ORT) can generate long postpacing intervals (PPI) that cause misdiagnosis of AV nodal reentrant tachycardia (AVNRT), despite correction for delay in the AV node (cPPI). [5][6][7] This study sought to evaluate the electrophysiological features and criteria differentiating the 4 atypical AV node-dependent long RP SVTs: atypical AVNRT, atypical AVNRT with a concealed, bystander NF AP (atypical AVNRT/NF AP), ORT using a concealed, slowly conducting, decremental AV AP (also called the permanent form of junctional reciprocating tachycardia [PJRT]), and ORT using a concealed NF AP (also called NF reentrant tachycardia [NFRT]