QRS voltage and cycle length alternation can be seen during supraventricular re-entrant tachycardias, especially in atrioventricular (AV) re-entrant tachycardia. We present a case of a 20-year-old man, in which AV nodal re-entrant tachycardia (AVNRT) shows alternation of QRS voltage and cycle length, as well as right bundle branch block aberration due to a re-entrant circuit using two distinct, beat-to-beat alternating slow AV nodal pathways antegradely and a single fast pathway retrogradely. Although more than one antegrade slow pathway exists, creation of a single lesion at the right posterior atrial septum using the conventional right-sided approach successfully eliminated AVNRT.