 This is a randomized, double-blind, placebo-controlled trial of ACE-I therapy in children less than 18 years of age with at least moderate MR who are at least 6 months postoperative from repair of an AVSD. A non-randomized Observational Phase enrolled 181 children who were less than 6 months postoperative from repair of an AVSD, who were then evaluated at 6 months for trial eligibility. 