The importance of atrial fibrillation has always motivated the search of new treatment alternatives. Internal cardioversion has been proposed as a choice in the treatment of atrial fibrillation, giving rise to the development of atrial defibrillator. We present the case of a 68 years old patient without structural heart disease and with diagnosis of chronic atrial fibrillation of 10 months of evolution. He received treatment with antiarrhythmic drugs and successful electrical external cardioversion, but he relapsed a week later. For this reason, we decided to perform internal cardioversion with an electrocatheter (DAIG) placed in the coronary sinus through the right jugular vein and under light sedation with propofol (2 mg/kg weight). We applied three shocks of 1, 3, and 5 joules, being able to convert to sinus rhythm without complications. The patient continues under treatment with antiarrhythmic agents. Internal cardioversion has shown to be an effective way for the treatment of chronic atrial fibrillation, using a light sedation and low energy level to reestablish the sinus rhythm.