AbstractRational management of pulmonary artery hypertension (PAH) in the newborn infant must be based on an understanding of underlying causes. When a specific diagnosis can be made, empirical treatment gives way to specific therapy. For every pathophysiologic abnormality potentially resulting in PAH, clinical entities can be identified and key therapeutic interactions can be considered.1. Pulmonary Venous Hypertension: PAH is secondary to obstruction of blood flow through the left heart. If based on anatomic abnormality (mitral or left atrial), surgical relief of obstruction is required. If PAH is the result or functional abnormality of the left ventricle (transient left ventricular ischemia), medical treatment of left ventricular failure is most important.2. Functional Obstruction of Pulmonary Vascular Bed: Hyperviscosity of blood (polycythemia ‐ HCT>65) results in increased pulmonary vascular resistance. Treatment consists of reduction of red blood cell volume.3. Pulmonary Vascular Constriction: Hypoxemia with or without pulmonary parenchymal disease (primary or secondary persistent fetal circulation [PFC] syndrome). Therapy is directed at improvement of oxygenation and dilatation of pulmonary arteriolar bed (e.g. O2hyperventilation and/or pulmonary vasodilator therapy).4. Decreased Pulmonary Vascular Bed: If primary pulmonary hypoplasia is present, no treatment is available. If secondary form (diaphragmatic hernia), surgical repair and pulmonary vasodilatation of contralateral lung is indicated. Extracorporeal membrane oxygenation (ECMO) can be used in severe cases.5. Increased pulmonary blood flow: Causes in the neonate include complex heart disease without pulmonary stenosis; and peripheral A—V fistula. Treatment: Surgical limitation of pulmonary blood flow may be required.Even when PAH is the result of combined etiologies, a prompt well‐organized clinical management plan can follow from understanding of pathologic princ