BACKGROUND: There is no clinical evidence supporting medical treatment for the failing systemic right ventricle in patients with transposition of the great vessels with atrial switch. Cardiac magnetic resonance studies have shown a significant degree of myocardial fibrosis in right ventricles in the systemic position, which predisposes to systolic and diastolic dysfunction. Aldosterone is a widely recognized neurohormonal marker involved in the formation of myocardial fibrosis and the treatment with aldosterone antagonists has shown a decrease in ventricular mass in hypertensive patients, presumably related to reduction of myocardial fibrosis.

HYPOTHESIS: Low dose of eplerenone, a selective mineralocorticoid receptor blocker, in patients with systemic right ventricle can reduce the ventricular mass by means of a reduction in myocardial fibrosis, resulting in improved systolic function.

PATIENTS AND METHODS: Randomized, double blind, parallel clinical trial comparing eplerenone (50mg daily) with placebo.

Study population: Adult patients (>18 years) diagnosed with repaired transposition of the great arteries with atrial switch (Senning or Mustard techniques) routinely followed at a tertiary referral center.

Duration: 12 months. Outcomes: Right ventricular mass, myocardial fibrosis mass and ejection fraction assessed by cardiac magnetic resonance.

Inclusion Criteria:

• Adult patients (>18 years old)
• Diagnosis of transposition of the great arteries repaired with atrial switch procedures (Mustard or Senning).
• Regular follow up at tertiary referral center.

Exclusion Criteria:

• Concomitant disease with life expectancy <1 year.
• Inclusion in heart transplant waiting list.
• Basal serum creatinine level > 1.5 mg/dl.
• Basal serum potassium level > 5.0 mmol/L.
• Intolerance to the investigational medical product.
• Treatment with spironolactone or eplerenone within the previous 6 months.
• Inability to undergo magnetic resonance imaging.
• Pregnancy or breast feeding.
• Denial of informed consent.