['The prognosis of patients with severe pulmonary hypertension (PHT) is poor. To determine prognosis and guide therapy, an acute hemodynamic trial of selective pulmonary vasodilators, usually inhaled nitric oxide (iNO), was performed. We hypothesized that oral sildenafil, a phosphodiesterase-5 inhibitor, is a safe and effective alternative to iNO.', 'We studied 13 consecutive patients (mean+/-SEM, 44+/-2 years of age; 9 women) referred for consideration of heart-lung transplantation or as a guide to medical therapy. All but one were functional class III or IV. Patients had primary PHT (n=9), pulmonary arterial hypertension (n=2), or secondary PHT (n=2). Hemodynamics and serum cyclic guanosine-monophosphate levels (cGMP) were measured at baseline and at peak effects of iNO (80 ppm), sildenafil (75 mg), and their combination. The decrease in pulmonary vascular resistance was similar with iNO (-19+/-5%) and sildenafil (-27+/-3%), whereas sildenafil+iNO was more effective than iNO alone (-32+/-5%, P<0.003). Sildenafil and sildenafil+iNO increased cardiac index (17+/-5% and 17+/-4%, respectively), whereas iNO did not (-0.2+/-2.0%, P<0.003). iNO increased, whereas sildenafil tended to decrease, pulmonary capillary wedge pressure (+15+/-6 versus -9+/-7%, P<0.0007). Systemic arterial pressure was similar among groups and did not decrease with treatment. cGMP levels increased similarly with iNO and sildenafil, and their combination synergistically elevated cGMP (P<0.0001).'] Is oral sildenafil an effective and specific pulmonary vasodilator in patients with pulmonary arterial hypertension : comparison with inhaled nitric oxide?