Inclusion Criteria:  Corrected gestational age (postmenstrual age) > 34 6/7 weeks postnatal age ≤ 28 d on respiratory support with invasive mechanical ventilation, non-invasive ventilation, CPAP or high flow nasal cannula (defined as flow rates ≥ 2 LPM with a humidifier), inspired oxygen concentration, FiO2 ≥ 0.3 and echocardiography shows any finding suggestive of PH (or score > 0 for PH in table 2). Infants with congenital diaphragmatic hernia (CDH), Down syndrome, hypoxic ischemic encephalopathy (HIE) on therapeutic hypothermia and patent ductus arteriosus (PDA), patent foramen ovale/atrial septal defect (PFO/ASD) and ventricular septal defect (VSD) (single or multiple) < 2 mm can be included in the study.  Exclusion Criteria:  < 32 weeks gestation at birth (31 6/7 or lower) Weight < 2000 g at the time of enrollment Severe HRF with OI > 35 or SpO2 < 75% on FiO2 = 1.0 on mechanical ventilation for > 60 minutes in spite of correction of reversible factors such as pneumothorax A condition or congenital anomaly known to be lethal (high likelihood of death during infancy) - e.g., trisomy 18 or trisomy 13 Congenital heart disease other than ASD/PFO, PDA or VSD (single or multiple defects) < 2 mm.