Some people are born with a birth defect where they only have one functioning ventricle (lower chamber) in their heart. This condition can be initially managed with a Fontan operation, but there is a risk of developing Fontan Circulatory Failure (FCF) later in life. FCF occurs when the single working heart ventricle is no longer strong enough to pump blood throughout the body. This also means the heart has difficulty supplying oxygen to keep up with the needs of the body. As a result, individuals living with FCF may have some challenges carrying out day to day activities. A heart transplant is currently the only therapeutic option for individuals living with FCF. The investigators are conducting this trial to determine whether a medication called empagliflozin can help these people have a better quality of life.

EMPA-HEART 3 CardioLink-12 is a global, multicentre, randomized, double-blinded, placebo-controlled, parallel group trial of empagliflozin vs. placebo in addition to standard of care therapy in adults with Fontan Circulatory Failure (FCF). A total of 410 individuals who provide written informed consent and meet the inclusion criteria following screening will be randomized (1:1) to receive either empagliflozin 10 mg once daily or matching placebo. During the 12-week follow-up, there will be four in-person and three telephone/virtual assessment visits.

The primary goal of this investigation is to determine whether 12 weeks of therapy with the sodium-glucose cotransporter 2 (SGLT2) inhibitor, empagliflozin, will improve clinical and participant-reported outcome measures in adults with FCF.

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