SGLT2 Inhibition With Empagliflozin in Fontan Circulatory Failure

Inclusion Criteria: * Adults (≥18 years of age) with FCF, defined by dysfunction of the Fontan physiology that causes limitation to the individual's ability to carry out daily life activities, on standard of care therapy Exclusion Criteria: * Diuretic initiation or dose change ≤2 weeks prior to enrollment On a SGLT2 inhibitor currently or within 12-weeks prior to enrollment in the trial * Allergic to or has a known intolerance to any of the ingredients in empagliflozin or other SGLT2 inhibitors * Pregnant or planning a pregnancy during the duration of the trial or breast feeding * Living with type 1 diabetes mellitus * Has an unresolved acute illness (e.g., acute appendicitis, COVID-19, gastroenteritis) * History of ketoacidosis * Has an estimated glomerular filtration rate (eGFR) that is \<30 mL/min/1.73 m2 Total bilirubin, alanine aminotransferase (ALT) or aspartate aminotransferase (AST) ≥2-fold upper limit of normal (ULN) at screening * Has a baseline systolic BP that is \<80 mmHg or ≥200 mmHg * Planned hospital intervention during trial period for management of FCF defined as one of the following: * Admission for intravenous diuretics * Admission for intravenous inotropes * Admission for ascites drainage * Admission for new or worsening ascites of clinical significance * Admission for management of arrhythmia * Admission for management of lymphatic dysfunction * Admission for interventional cardiological or cardiac surgical procedure within 30-days prior to screening, or consideration for any cardiac surgical or interventional cardiological procedure during trial participation * Admission for cardiac resynchronization therapy within 90-days prior to screening, or consideration of cardiac resynchronization therapy during trial participation * Is unable to provide written informed consent, complete the trial or comply with the requirements of the trial protocol * Participation in other interventional studies within 30-days of the screening visit that could influence any of the trial outcomes (exclusive of observational registries) * Received intravenous diuretic within the previous 14-days * On a heart transplant waiting list * Current or imminent hospitalization for management of FCF