Background: Although radiofrequency catheter ablation of atrial flutter is associated with a high rate of initial success, several clinical issues regarding this therapy remain to be defined. For example, the risks of recurrent atrial flutter and of developing atrial fibrillation after flutter ablation are unknown. In addition, it is not known whether elimination of atrial flutter will modify the natural history of atrial fibrillation in patients who experience both of these arrhythmias. The purpose of the present study was to determine the actuarial freedom from recurrent or new atrial arrhythmias in patients with atrial flutter undergoing catheter ablation. Methods and Results: The study population consisted of 59 consecutive patients (mean age, 61.9±12.6 years) with typical atrial flutter who underwent catheter ablation of the reentrant circuit. Catheter ablation was not advised for patients in whom paroxysmal atrial fibrillation had been a major clinical problem. The inducibility of atrial fibrillation and atrial flutter was assessed after successful atrial flutter ablation with programmed atrial stimulation and rapid atrial pacing to a cycle length of 180 ms or 2:1 atrial capture. Atrial flutter was successfully ablated and rendered noninducible in 53 of 59 patients 190%). Over a mean follow up period of 13.2±6.6 months, atrial flutter recurred in 5 patients (9.4%). Atrial fibrillation occurred in 14 of 53 patients after successful ablation (26.4%). Four clinical variables were associated by univariate analysis with the late occurrence of atrial fibrillation: (1) the presence of structural heart disease, 121 a history of atrial fibrillation before ablution of atrial flutter, (3) inducible sustained atrial fibrillation after ablution, and (4) a greater number of failed antiarrhythmic drugs. By multivariate analysis, only the persistent inducibility of sustained atrial fibrillation predicted the later development of atrial fibrillation. Conclusions: Although atrial flutter ablation is highly effective and associated with a low risk of recurrent atrial flutter, atrial fibrillation continues to be a long-term risk for individuals undergoing this procedure. The risk of later atrial fibrillation is especially high for patients in whom sustained atrial fibrillation remains inducible after ablution of atrial flutter.