Synchronized electrical cardioversion is a tool used to restore normal sinus rhythm in canine patients with arrhythmias. The most common arrhythmias treated with cardioversion are atrial fibrillation and atrial flutter. Cardioversion is proven to be a safe and effective technique in these patients, who often have significant underlying heart disease. Cardioversion is performed under general anesthesia and can be accomplished on an outpatient basis. After the induction of anesthesia, we use the cardioverter to send a a biphasic electrical current to the heart and this serves to reorganize the electrical activity in the cardiac atria. The restoration of normal sinus rhythm can lead to a better quality of life and improved exercise tolerance in these patients.