The incidence of congenital heart disease is approximately 8/1,000 live births and appears to be constant around the world. The currently accepted paradigm for the development of pulmonary vascular disease associated with congenital heart disease maintains that increased pulmonary blood flow and pressure trigger unfavorable vascular remodeling. Endothelial cell dysfunction, abnormal shear stress, circumferential wall stretch, and an imbalance in vasoactive mediators conspire to promote vasoconstriction, inflammation, thrombosis, cell proliferation, impaired apoptosis, and fibrosis. We estimate that worldwide 3 million children are at risk for the development of pulmonary vascular disease due to congenital heart disease. The majority of children at risk globally will have a reparable heart defect, such as an isolated atrial septal or ventricular septal defect or patent ductus arteriosus. Cardiac repair in the first 2 years of life would prevent the development of Eisenmenger syndrome, the most advanced form of pulmonary vascular disease secondary to congenital heart disease. Worldwide, only a small fraction of those at risk are offered surgical repair. Thus, access to timely medical care would eliminate the vast majority of suffering, disability, and death from Eisenmenger syndrome. Globally, pulmonary vascular disease associated with congenital heart disease may be the most preventable cause of pulmonary artery hypertension and related mortality and morbidity.