Congenital Heart Disease

A congenital heart defect may be quiet during fetal life and then become an emergency within hours of birth. The lungs expand, pulmonary vascular resistance falls, the foramen ovale functionally closes, and the ductus arteriosus begins to constrict. Those changes expose a circulation that had depended on fetal shunts. The bedside question is therefore more specific than “Is the newborn cyanotic?” Ask which pathway is failing: systemic blood flow, pulmonary blood flow, or mixing of oxygenated and deoxygenated blood. Duct-dependent lesions can deteriorate when the ductus closes; large left-to-right shunts often declare themselves later through pulmonary overcirculation and heart failure. This model makes the timing, assessment findings, and urgency of treatment more predictable.