A male infant presented at birth with severe coarctation of the aorta and marginal left ventricular and mitral valve dimensions associated with a large secundum atrial septal defect. Following successful arch repair, the left ventricle remained small with preferential left-to-right atrial shunting and a dilated right ventricle. Clinically, the infant continued with tachypnea, poor feeding, and failure to thrive. At 4 months of age, the defect was closed with an Amplatzer Atrial Septal Occluder which resulted in immediate left ventricular cavity enlargement and clinical improvement.