Study design: a prospective, multicenter, double-blind, randomized, placebo-controlled trial. Follow up two years Study population: adult patients with Tetralogy of Fallot with right ventricular dysfunction, defined as right ventricular ejection fraction < 50% and without severe valvular lesions Intervention: patients are randomized to receive either losartan 150 mg once daily, or placebo in the same regimen. Main study parameters/endpoints: the primary endpoint is difference in change in RV ejection fraction, determined by cardiovascular magnetic resonance imaging (CMR), between the treatment and the control group at two years follow-up.