Persistent pulmonary hypertension of the newborn (PPHN) is the failure of the pulmonary vascular resistance to decrease after birth, resulting in right-to-left shunting of blood and hypoxemia. It can be primary or secondary to conditions like meconium aspiration syndrome, asphyxia, or lung hypoplasia. Diagnosis involves signs of cyanosis and hypoxemia unresponsive to oxygen. Treatment aims to maintain oxygenation through supportive care, vasodilator drugs like inhaled nitric oxide, high frequency ventilation, and in severe cases, extracorporeal membrane oxygenation.