The case of a 16-year-old have pointed out the role of the isthmus between the lower left pulmonary vein and the mitral annulus in determining features of retrograde atrial activation, during ablation of a left lateral accessory pathway.This article reports a case of atrioventricular tachycardia generated by a single left anterolateral accessory pathway with exclusive retrograde conduction where radiofrequency current, applied to the lateral wall of the mitral annulus, produced diverse patterns of retrograde atrial activation. Potential electrophysiologic mechanisms at the root of observed peculiarities are discussed. Case reportA 16-year-old female patient who had experienced recurrent supraventricular tachycardia since the age of 6 underwent invasive electrophysiologic examination and radiofrequency (RF) catheter ablation.The procedure was performed with the patient sedated with intravenous fentanyl and midazolam. Through a puncture in the right femoral vein, three 6-French quadripolar catheters with 5-mm electrode spacing (Response TM