A Study to Evaluate MEDI-524 In Children With Hemodynamically Significant Congenital Heart Disease

Inclusion Criteria: * 24 months of age or younger at randomization (child must have been randomized on or before their 24-month birthday) * Documented, hemodynamically significant CHD * Unoperated or partially corrected CHD * Written informed consent obtained from the patient's parent(s)/legal guardian(s) Note: The following children were not eligible: children with uncomplicated small atrial or ventricular septal defects or patent ductus arteriosus, children with aortic stenosis, pulmonic stenosis, or coarctation of the aorta alone. Children with acyanotic cardiac lesions must have pulmonary hypertension \[≥ 40 mmHg measured pressure in the pulmonary artery (PA)\] or the need for daily medication to manage CHD. Exclusion Criteria: * Unstable cardiac or respiratory status, including cardiac defects so severe that survival was not expected or for which cardiac transplantation was planned or anticipated * Hospitalization, unless discharge was anticipated within 21 days * Anticipated cardiac surgery within two weeks of randomization * Requirement for mechanical ventilation, extracorporeal membrane oxygenation, continuous positive airway pressure or other mechanical respiratory or cardiac support * Associated non-cardiac anomalies or end organ dysfunction resulting in anticipated survival of less than six months or unstable abnormalities of end organ function * Acute respiratory illness, or other acute infection or illness Note: children with any respiratory symptoms must have had a negative RSV test prior to randomization * Chronic seizure or evolving or unstable neurologic disorder * Known immunodeficiency * Mother with HIV infection (unless the child had been proven to be not infected) * Known allergy to Ig products * Receipt of any polyclonal antibody (for example, Hepatitis B IG, IVIG, VZIG) within 3 months prior to randomization * Receipt of palivizumab (Synagis®) within 3 months prior to randomization * Use of investigational agents within the past three months (other than investigational agents commonly used during cardiac surgery or the immediate post-operative period, e.g., nitric oxide) * Current participation in other investigational protocols of drugs or biological agents * Previous participation in MI-CP124 (Season 1)