Ectopic atrial tachycardia (EAT) is a rare but reversible cause of dilated cardiomyopathy (DCMP). The diagnosis and the definite control of the arrhythmia are essential for the regression of DCMP. Unfortunately, conventional antiarrhythmic drugs usually fail to control the arrhythmia, and the results of surgery or direct current ablation are suboptimal. Recently, radiofrequency (RF) catheter ablation has been evolving as a safe and effective therapy for EAT. This report describes the RF ablation treatment of a 14-year-old boy with DCMP secondary to chronic EAT. Activation mapping was used for the purpose of identifying the focus origin located just anterior to the coronary sinus os. RF energy applied at this focus successfully terminated the tachycardia. No complications related to the procedure were observed. RF ablation not only caused elimination of the EAT but also led to improvement in left ventricular function as early as two weeks after the procedure, and complete resolution of DCMP in three months.