Sinus node dysfunction may predispose Fontan patients to atrial tachyarrhythmias, the most common being macro-reentrant circuits or intra-atrial reentrant tachycardia.S4.4.2-13,S4.4.2-47 Nearly 90% of Fontan patients who die from HF have coexisting atrial tachyarrhythmias.S4.4.2-48 Fontan patients are at increased risk of complica- tions from antiarrhythmic therapy, such as tors- ades de pointes with dofetilideS4.4.2-49 and amio- Such agents should be used cautiously and in consultation with ACHD cardiologists and electrophysiology specialists with expertise in ACHD. 2. Serial imaging can be valuable for assessing many of the long-term sequelae of Fontan palliation such as thrombosis, right-to-left shunts (eg, fen- estration, intrapulmonary AV malformation), ob- structive lesions, systemic AV valve dysfunction, diastolic or systolic ventricular function, collat- eral burden, and branch PA obstruction. Imaging can be challenging and requires informed un- derstanding about the patient's particular situa- tion. Although CCT is possible in patients with Fontan physiology, it is challenging to ensure contrast dispersal through the pulmonary vas- culature because of streaming of venous return to the PA from multiple separate sources (eg, superior vena cava, inferior vena cava right atrium 3. Hemodynamic assessment, particularly of the pul- monary circulation, is crucial to making informed decisions about the type and timing of surgical intervention. 4. Hemodynamic problems may first manifest through arrhythmia. Thus, first presentation of arrhythmia should warrant thorough review of the patient s Fontan circulation and ventricular function. 5. Aerobic exercise may help maintain respiratory mechanics, which can improve transpulmonary flow in the Fontan circulation. Stroke volume dur- ing exercise and exercise capacity are directly re- lated to skeletal muscle function. Consequently, strength training may improve exercise capacity in patients with Fontan palliation. 6. 