Fig. 1. Percent change of pulmonary arterial pressure (PAP) and systemic arterial pressure (SAP) after administration of increasing doses of sildenafil. Cumulative doses of 12.5, 25, and 50 mg sildenafil caused a significant reduction in PAP. Systemic hemodynamics were not altered, except for a 12% decrease of SAP at a dose of 50 mg sildenafil. *P < 0.05, **P < 0.01, and ***P < 0.001 versus baseline values during U46619-induced acute pulmonary hypertension (n = 5). Data are expressed as mean ± SE.