Radiofrequency (RF) catheter ablation of atriofascicular accessory pathways (AP) characterized by decremental antegrade conduction property and result in antidromic tachycardia with left bundle branch morphology is a current preferred theurapetic approach. Two patients, who were twenty-two and thirty-six years old, with atriofascicular AP and drug-resistant antidromic tachycardia were hospitalized for RF catheter ablation. In the first case, cardiac mapping was performed during antidromic tachycardia. While mapping using a long sheath through posterolateral tricuspid annulus, AP conduction was seen to cease temporarily during catheter manipulations. AP was succesfully ablated by RF currents delivered at the same location. In the second case, mapping was done during atrial pacing. AP was ablated through the posterolateral tricuspid annulus where the conduction was terminated during the manipulation of catheter. In both cases, as the RF current was delivered, irregular Mahaim automatic tachycardia occurred with a similar QRS morphology to antidromic tachycardia. They were free of symptoms for about 3 months in the first case and 2 months in the second case.