OBJECTIVE Different vasodilators and different routes of application are used for the treatment of primary pulmonary hypertension (PPH). Recently, sildenafil, a phosphodiesterase-V inhibitor, has been shown to have beneficial hemodynamic effects in PPH. However, the hemodynamic effects of sildenafil have not been characterized and compared to other vasodilators such as inhaled nitric oxide (iNO) or iloprost in PPH in the same group of patients. METHODS We investigated prospectively 10 consecutive patients with PPH using iNO, iloprost aerosol, and oral sildenafil to test acute hemodynamic response during right-heart catheterization. RESULTS iNO, iloprost aerosol, and sildenafil caused a significant fall of mean pulmonary artery pressure and pulmonary vascular resistance (PVR) [p < 0.05]. Correspondingly, cardiac output and mixed venous saturation increased slightly in all groups. Systemic arterial pressure and vascular resistance were mainly unaltered. Using a PVR reduction of > or =20% to define a significant response, 7 of 10 patients were responders to iloprost aerosol, whereas 4 of 10 patients responded to iNO and oral sildenafil. Improvement of oxygenation as indicated by an increase of arterial oxygen tension was observed with iloprost aerosol (p < 0.01). CONCLUSIONS All of the three substances, iNO, iloprost aerosol, and oral sildenafil, significantly improved pulmonary hemodynamics in patients with PPH. The most prominent hemodynamic effects and improvement of oxygenation were observed with iloprost aerosol.