This study will enroll premature newborns who require extra oxygen but do not require intubation or mechanical ventilation for respiratory failure in the first 72 hours of life. Participants will be randomly assigned to receive low-dose, non-invasive iNO or nitrogen (placebo) during their hospital stay. While hospitalized, participants' heart rate, blood oxygen level breathing rate, blood pressure, and medications will be monitored, and blood collection will occur at various times. Monitoring will continue until participants are 30 weeks corrected gestational age or for at least 14 days if participants are born at 29 weeks or more. All participants will undergo an ultrasound of the head when they are 7 days, 28 days, and 36 weeks of age. They will undergo an echocardiogram, which is an ultrasound of the heart, at 7 and 21 days of age and 4 weeks before the original expected due date. A chest x-ray will be performed before hospital discharge, and a breathing status test will be performed either 4 weeks before participants' original expected due date or before hospital discharge. Follow-up study visits will occur at Years 1 and 2, and will include a physical examination and developmental and behavioral testing. Another echocardiogram will also be performed at the Year 1 visit.