Angiotensin-Converting Enzyme (ACE) inhibitor cessation in the setting of well-functioning Fontan hearts

INTERVENTION: This is a post‐marketing, prospective, multi‐centre, parellel design, open‐label randomised single‐blinded equivalence trial of angiotensin‐converting‐enzyme inhibitor (ACEI) or angiotensin II receptor blockers (ARB) cessation versus continuation in people greater than 8 years old with a Fontan circulation and preserved ventricular systolic function. The intervention group will cease their ACEI or ARB medication for 12 months. The intervention will not be personalised but adherence will be measured using a medication diary. CONDITION: congenital heart defect PRIMARY OUTCOME: VO2 peak within 5% range measured by cardiopulmonary exercise testing. SECONDARY OUTCOME: Arrhythmia assessed using ECG as part of the cardiopulmonary exercise test Blood pressure assessed with blood pressure monitor Death Degree of AV valve regurgitation assessed using Echocardiogram Heart failure assessed by taking medical history during clinical assessment and patient medical records Hospitalisation assessed by taking medical history during clinical assessment and patient medical records N‐terminal prohormone of brain natriuretic peptide (NT‐proBNP) levels calculated using a blood test. NYHA class assessed using Specific Activity Scale Quality of life assessed using PedsQL, CHU‐9D, EQ‐5D‐3L and TBQ Ventricular function assessed using Echocardiogram INCLUSION CRITERIA: 1. Have a Fontan circulation 2. Are taking ACEI or ARB medication for 12 months or more. 3. Can perform a cardiopulmonary exercise test on a cycle ergometer.