A 55-year-old man was referred because of congestive heart failure and atrial flutter. A 12-lead electrocardiogram (ECG) showed positive P waves in leads II, III, and aVF with a continuously undulating pattern that lacked an isoelectric baseline. Tachycardia was diagnosed as atypical atrial flutter based on classical criteria. An electrophysiological study and catheter ablation using an electroanatomical system revealed the mechanism of the tachycardia to be focal atrial tachycardia originating from the left atrial roof. This case indicates that focal atrial tachycardia may present as atypical atrial flutter on the surface ECG.