A 60-year-old woman was referred for catheter ablation of atrial fibrillation (AF). Atrial flutter and atrial tachycardia (AT) also had been clinically documented. During the electrophysiological study, the clinical AT was induced by burst atrial pacing during isoproterenol infusion and exhibited negative P waves in the inferior leads, positive P waves in leads I, aVL, and aVR, and biphasic P waves in lead V1. The AT repeatedly and spontaneously accelerated to initiate AF by causing fibrillatory conduction in the atria. Successful catheter ablation of the AT was achieved in the non-coronary cusp of the aorta (NCC) where the local atrio-ventricular electrogram amplitude ratio was >1 during both the AT and sinus rhythm. The tailored approach targeting the NCC AT alone without left atrial ablation completely eliminated the AF. In catheter ablation of AF in a patient with a co-existing clinical AT, it may be recommended to examine the clinical AT first. If the clinical AT initiates the AF and local atrial activations in the His bundle region precede the P wave onset during AT, mapping in the NCC should be considered prior to left atrial catheterization.