Pulmonary hypertension may be encountered in the pediatric and neonatal intensive care unit. Managing these patients in the intensive care unit can prove extremely challenging, particularly when they become hemodynamically unstable. Pulmonary hypertension in pediatric patients is frequently associated with critical illnesses such as congenital heart disease, acute respiratory disease, and left heart failure. In neonates, pulmonary hypertension is idiopathic or related to respiratory distress or congenital heart failure. This review discusses the pathogenesis and physiology of pulmonary hypertension, the cardiopulmonary interactions in this pathology, and the adaptation to extra-uterine life.