Infants with congenital diaphragmatic hernia (CDH) usually have pulmonary hypoplasia and persistent pulmonary hypertension of the newborn (PPHN) leading to hypoxemic respiratory failure (HRF). Pulmonary hypertension associated with CDH is frequently resistant to conventional pulmonary vasodilator therapy including inhaled nitric oxide (iNO). Increased pulmonary vascular resistance (PVR) can lead to right ventricular overload and dysfunction. In patients with CDH, left ventricular dysfunction, either caused by right ventricular overload or a relative underdevelopment of the left ventricle, is associated with poor prognosis. Milrinone is an intravenous inotrope and lusitrope (enhances cardiac systolic contraction and diastolic relaxation respectively) with pulmonary vasodilator properties and has been shown anecdotally to improve oxygenation in PPHN. Milrinone is commonly used during the management of CDH although no randomized trials have been performed to test its efficacy. Thirty percent of infants with CDH in the Children's Hospital Neonatal Database (CHND) and 22% of late-preterm and term infants with CDH in the Pediatrix database received milrinone. In the recently published VICI trial, 84% of patients with CDH received a vasoactive medication. In the current pilot trial, neonates with an antenatal or postnatal diagnosis of CDH will be randomized to receive milrinone or placebo to establish safety of this medication in CDH and test its efficacy in improving oxygenation.