Patients with a failing Fontan frequently have dysrhythmias. This review will focus on the treatment of those dysrhythmias based on the 140 patients who have had a Fontan conversion with arrhythmia surgery at Ann & Robert H. Lurie Children's Hospital of Chicago (Chicago, IL). Important technical points to be emphasized are the following:* Atrial fibrillation is extremely common in patients with a failing Fontan and strong consideration should be given to a Cox-maze III during any Fontan conversion* Sinus node dysfunction is common post-conversion and all patients should receive a dual-chamber epicardial pacemaker* Careful preoperative imaging with either computed tomographic or magnetic resonance imaging is needed to predict re-entry problems at the time of repeat sternotomy* If the patient has protein-losing enteropathy, ascites, or a right or indeterminate ventricular morphology, strong consideration should be given to heart transplantation rather than a Fontan conversion and arrhythmia surgery. Freedom from cardiac death or transplant for patients undergoing Fontan conversion with arrhythmia surgery is 84% at 10 years. The effects of atrial arrhythmia operations are durable in most patients. There is increasing evidence that earlier referral of patients with an atriopulmonary Fontan for Fontan conversion will improve long-term results. Fontan conversion should be performed at centers with the institutional expertise to care for these complex patients. Note that this is an eroding patient population. The time to act may be now.