Introduction: We hereby present the case of a 74 year old patient with a dual-chamber pacemaker implanted 2 years before who came to the ER for fatigue and dizziness. Methods: Clinical examination revealed an AV rate of 140 bpm, BP = 90/60 mm Hg, while 12-lead ECG showed atrial tachycardia with a negative p-wave in the inferior leads and paced QRS complex. The differential diagnosis of pacemaker mediated tachycardia was excluded by the persistence of atrial tachycardia after inhibition of ventricular pacing. The patient was referred for EP study. Mapping of the right atrium revealed an atrial tachycardia with first activation at the level of the CS ostium. Considering the differential diagnosis pacing maneuvers were performed indicating AVNRT. Results: Radiofrequency ablation of the slow pathway was performed with termination of the tachycardia and stable sinus rhythm. Pacemaker controls performed during subsequent months (1, 3, 6, 12 months) revealed a persistent sinus rhythm.