Radiofrequency catheter ablation seems to become a first-line therapy for patients with paroxysmal tachycardias using an accessory pathway. We report the case of a 31-year-old woman who suffered from drug-resistant recurrent reciprocating tachycardia, using an uncommon accessory pathway. The 12-lead electrocardiogram in sinus rhythm showed the following characteristics: a positive delta waves in leads I, II, aVL, aVF, QRS axis = 0 degrees, R/S in lead V1 < 1, and a special QRS pattern in the precordial leads (QS or Qr in V1-V3 and QRS transition > V3). A deep septal parahissian accessory pathway has been localized using classic endocardial mapping procedures and has been confirmed during successful radiofrequency catheter ablation. Normal auriculo-ventricular conduction has been totally preserved. No complications or recurrence were observed during the follow-up. We have reviewed the electrophysiologic criteria to confirm this rare accessory pathway location.