The Effects of Eplerenone on Markers of Myocardial Fibrosis in Adult Congenital Heart Disease

Hypothesis: By blocking aldosterone signaling in patients with Tetralogy of Fallot, Transposition of the great vessels with a prior atrial switch, and single ventricle "Fontan" patients, incident heart failure will be delayed, symptoms of heart failure ameliorated, and risk of arrhythmias decreased through decreases in myocardial fibrosis. Half of enrolled patients will complete an SF-36 quality of life questionnaire, perform a 6 minute walk, and have blood drawn for biomarker analysis at enrollment, again after 3 months without therapy, after 6 months on therapy, then finally after 12 months of eplerenone therapy. Half of enrolled patients will have the 3 month drug free period at the end of 12 months on therapy. Patients will be randomly assigned to drug free period up front versus at the conclusion of the trial period. Eplerenone will be started at a dose of 25mg and titrated up to 50mg at 4 weeks if tolerated. Blood will be drawn for basic metabolic panel analysis at enrollment, 3 months, 4 months to allow for dose titration, and at 6 and 12 months for monitoring.