IIa C-LD Catheter ablation can be useful in adults after Fontan palliation with intra-atrial reentrant tachycardia or focal atrial IIa C-LD Fontan revision surgery, including arrhythmia surgery as indicated, is reasonable for adults with atriopulmonary Fontan connections with recurrent atrial tachyarrhythmias refractory to pharmacological therapy and catheter ablation who have preserved systolic ventricular function and severe atrial IIa B-R Pulmonary vasoactive medications can be beneficial to improve exercise capacity in adults with Fontan repair.S4.4.2-19 S4.4.2-25 IIb B-NR Antiplatelet therapy or anticoagulation with a vitamin K antagonist may be considered in adults after Fontan palliation without known or suspected thrombus, thromboembolic events, or prior IIb C-LD Reoperation or intervention for structural/ anatomic abnormalities in a Fontan palliated patient with symptoms or with failure of the Fontan circulation may be Synopsis Fontan repairs are the most common palliation of sin- gle ventricle physiology seen in adults. The physiology is complex, with long-term consequences related to the obligatory elevation in central venous pressure and reduced cardiac output. Proposed medical therapy for the failing Fontan, which may manifest as protein- losing enteropathy, hepatic dysfunction, lower extrem- ity venous congestion, and/or exercise limitation, has included many different modalities, although there is limited proven benefit in published research. Options for medical therapy include aldosterone antagonists or subcutaneous unfractionated heparin, which may sta- bilize the proteoglycan layer of the gut. PAH therapies are of increasing interest. Endothelin antagonists have been studied in a single RCT, which showed improved exercise capacity in 75 subjects randomized to bosen- tan compared with placebo.S4.4.2-19 Two other small non- randomized studies demonstrated minimal response to Corticosteroids, specifically budesonide, may be helpful for Fontan patients with hypoalbuminemia in the setting of protein-losing enteropathy poorly re- sponsive to other therapies. 