The hemodynamic and clinical features of congenital heart disease are dynamic. They are closely related to the normal maturational changes in the small pulmonary blood vessels, which, in turn, are influenced by the presence of certain congenital anomalies. The role of left atrial and pulmonary venous hypertension, possibly with associated hypoxia, in maintaining an elevated pulmonary vascular resistance, has been considered; and the relationship between cardiac failure, left atrial pressure elevation, and pulmonary hypertension, discussed. Evidence has been presented demonstrating the importance of normal sympathetic nervous system activity and of catecholamine release, in the adaptation of the circulation to a large volume overload associated with left-to-right shunt.