Atrial fibrillation (AF) is the most common arrhythmia in clinical practice. Cardioversion for AF may be performed by either using direct current (DC) shock (electrical cardioversion) or using drugs (chemical cardioversion). Here we report a case of a patient with heart failure and AF, who reverted to the normal sinus rhythm on correction of hyperkalemia (electrogenic cardioversion). The patient maintained sinus rhythm during follow-up. We highlight the importance of serum potassium in patients with AF.