Objective: The objective of this study is to determine the effects that sildenafil citrate has on gas exchange in infants with bronchopulmonary dysplasia (BPD)-associated pulmonary hypertension (PH).Study Design: A retrospective review was performed from 2005 to 2009. Infants treated with sildenafil citrate for greater than 48 h were included. Standard patient data was collected, including echocardiogram, inspired oxygen and systemic blood pressure, before and during administration of sildenafil citrate.Result: Sildenafil citrate was used in 21 preterm infants with BPDassociated PH. A significant reduction in estimated right ventricular peak systolic pressure was seen after initiation of sildenafil citrate, with the majority of infants showing no improvement in gas exchange at 48 h of treatment. Four infants died during treatment. Conclusion:Sildenafil citrate reduced estimated pulmonary artery pressures, but this reduction was not reflected in improved gas exchange within the first 48 h.