Abstract Continuous intravenous (IV) sildenafil may avoid the acute systemic vasodilatory effects of bolus dosing in infants with pulmonary hypertension (PH). We aimed to examine the tolerability of different methods of IV sildenafil administration. Methods: We retrospectively evaluated subjects less than 12 months old with PH, who had been started on IV sildenafil. Vital signs, oxygen requirement, and vasoactive-inotropic score (VIS) before and after sildenafil initiation were noted, as was the need for discontinuation due to side effects. Results: Forty-three subjects were identified (23 continuous, 20 intermittent dosing). There were no statistically significant differences between groups in gender or gestational age, but higher baseline inspired oxygen (FiO2) and VIS in the continuous group suggested a higher baseline severity of illness (p=0.012). After sildenafil initiation, there were no significant differences in the change in blood pressure, oxygen saturation, FiO2, or VIS between groups, and no difference in the number of subjects requiring discontinuation due to side effects (4 in the continuous group, 1 intermittent, p=0.35). Eight subjects (34.8%) in the continuous group and 3 (15%) in the intermittent group died (p=0.024). Conclusions: In this small cohort of infants with PH treated with continuous or intermittent IV sildenafil, there were no statistically significant differences between groups in the change in vital signs, VIS, and oxygen requirement, or the need for discontinuation of therapy due to side effects. A higher mortality rate in the continuous infusion group may be explained by higher baseline illness severity.