Differentiating atypical atrioventricular nodal reentrant tachycardia (AVNRT) from septal orthodromic reentrant tachycardia (ORT Septal ) is challenging in nonsustained tachycardia. When sustained, the postpacing interval minus tachycardia cycle length following entrainment (PPI Entrainment − TCL) and stimulation to atrial interval minus ventriculoatrial interval (Stim-A Entrainment − VA) are utilized. We hypothesized that the first tachycardia cycle after tachycardia induction with right ventricular apical extrastimulation would yield comparable information to entrainment, precluding the need for sustained tachycardia. Twenty-four patients with AVNRT (age 47 ± 18 years), 19 with ORT Septal (age 42 ± 17 years), and 15 with ORT over a left lateral accessory pathway (ORT Left ) (age 41 ± 16 years) were included. The ventricular extrastimulus to atrial depolarization at tachycardia initiation (Stim-A Initiation ) and tachycardia VA interval were measured to establish the Stim-A Initiation minus VA interval (Stim-A Initiation − VA). The ventricular extrastimulus to the subsequent right ventricular apical depolarization (postpacing interval at initiation, PPI Initiation ) was utilized to obtain the PPI Initiation minus TCL (PPI Initiation − TCL). The AH interval associated with the PPI Initiation minus the AH in tachycardia was utilized to establish a corrected PPI Initiation minus TCL (cPPI Initiation − TCL). The intervals after tachycardia initiation were longer for AVNRT than for ORT: mean PPI Initiation − TCL (193 ± 44 vs 91 ± 73; P <.001), cPPI Initiation − TCL (174 ± 44 ms vs 88 ± 50 ms; P <.001), and Stim-A Initiation − VA (161 ± 45 ms vs 69 ± 53 ms; P <.001). The correlation coefficient for Stim-A Initiation minus VA against Stim-A Entrainment minus VA was 0.79 and for cPPI Initiation minus TCL against PPI Entrainment minus TCL was 0.71. cPPI Initiation minus TCL <115 ms or Stim-A Initiation − VA <85 ms was observed only in ORT. The converse was observed in AVNRT but also in ORT Septal over decremental accessory pathways and ORT Left . Stim-A Initiation − VA < 85 ms or cPPI Initiation − TCL < 115 ms excludes AVNRT.