ARNI Versus plAcebo in Patients With Congenital sYStemic Right Ventricle Heart Failure

Inclusion Criteria: * Age \> or egal18 years with clinical follow-up at the Montreal Heart Institute Adult Congenital Heart Center * Systemic right ventricle (transposition of great vessels and atrial switch or congenitally corrected transposition of great vessels) * Moderate to severe systemic right ventricle dysfunction by transthoracic echocardiography (TTE) or right ventricle ejection fraction (RVEF) \<40% by MRI * NYHA Functional class II-III symptoms or peak exercise capacity \<80% of predicted on a previous standard treadmill exercise stress test (usually done every two years in our congenital clinic). * Ability to provide informed consent to the study * Access or own a telephone and/or access to internet connection for teleconference call * Own a mailing address to receive the medication by post (FedEx or Dicom) * Able to perform self-measurement of the blood pressure using Upper Arm Digital Blood Pressure Monitor as recommended by Hypertension Canada. Exclusion Criteria: * Participation in a clinical trial of an investigational drug, concurrently, or within the last 30 days prior enrolment * Planned cardiac surgery (e.g., severe tricuspid regurgitation with planned tricuspid valve replacement or repair) * Previous cardiac transplantation, or on heart transplant wait list * Myocardial infarction, stroke, or open-heart surgery in the previous 4 weeks * NYHA Functional class I or IV symptoms * Symptomatic hypotension (fainting, dizziness, lightheadedness, blurred vision, weakness, fatigue, nausea, palpitations, and headache) with a systolic blood pressure \<100 mmHg at screening, or asymptomatic \<90 mmHg at screening * eGFR \<30 mL/min/1.73 m2 * Reduction in eGFR \>35% from screening to randomization * Potassium \>5.2 mmol/L at screening or \>5.4 mmol/L at randomization * Known history of angioedema related to previous ACEI or ARB therapy or patients with a history of hereditary or idiopathic angioedema. * Patients who require concomitant treatment with an angiotensin converting enzyme inhibitor (ACEI) or an angiotensin receptor blocker (ARB) or a renin inhibitor for other indication than heart failure * Evidence of hepatic disease as determined by any one of the following: serum glutamate oxaloacetate transaminase (SGOT) or serum glutamate pyruvate transaminase (SGPT) values exceeding 3x upper limit of normal, bilirubin \>1.5 mg/dl at screening. * Unacceptable side effects with ACE-inhibitors or ARBs * Patient known with bilateral renal artery stenosis * Cyanosis; substantial left-to-right shunting (Qp/Qs \>1.5); severe mitral, aortic, or pulmonary regurgitation; systemic or pulmonary inflow obstruction with a peak velocity \>1.5 m/s by transthoracic echocardiography; and severe outflow tract obstruction with a peak systolic gradient \>80 mm Hg. * Inability to provide informed consent * Unable to exercice * Pregnant or planned pregnancy during the study * Breastfeeding * Severe pulmonary hypertension defined as pulmonary pressure egal or superior to systemic pressure