Atrial fibrillation (AF), a common arrhythmia in clinical practice, is associated with hemodynamic impairment of cardiac function, increased risk of serious thromboembolic events,1 and 1.5 to 1.8 times increased mortality.2 Restoration of sinus rhythm is the desirable end point in patients with AF. Transthoracic electrical cardioversion is currently a safe and effective method to restore sinus rhythm, yet its efficacy is limited, especially in cases with AF duration more than 36 months and left atrial size more than 60 mm.3-5 Studies in animals and humans have shown that internal cardioversion has a higher success rate compared to that of transthoracic cardioversion.6-8 We present two special cases with atrial fibrillation of long duration or refractory to transthoracic cardioversion that were successfully converted by a newly developed low energy internal cardioversion technique.