Background: Inhaled treprostinil was recently developed for the treatment of pulmonary arterial hypertension (PAH). We investigated the safety and acute haemodynamic effects of the combination oral sildenafil and inhaled treprostinil in an open label study in patients with precapillary pulmonary hypertension. Methods and patients: Inhaled nitric oxide (20 ppm; n=50), sildenafil (50 mg; n=50) and inhaled treprostinil (15 μg; n=25 or 30 μg; n=25) were applied in subsequent order during right heart catheter investigation to consecutive patients with pulmonary arterial hypertension (PAH; n=28), non-operable chronic thromboembolic pulmonary hypertension (CTEPH; n=17) and pulmonary fibrosis associated pulmonary hypertension (n=5). Results: Inhaled nitric oxide reduced pulmonary vascular resistance (PVR) to 87.3±5.1% of baseline values, reduced mean pulmonary arterial pressure (PAP) to 89.7±3.5% and increased cardiac output (CO) to 102.4±2.9%. Sildenafil reduced PVR to 80.1±5.0%, mPAP to 86.5±2.9% and increased CO to 103.8±3.2%. Treprostinil, inhaled 1 h after sildenafil, reduced PVR to 66.3±3.8%, mPAP to 77.8±3.3%, and increased CO to 107.1±3.3% (mean±95% confidence interval). Subgroup analysis showed similar acute haemodynamic effects in PAH and CTEPH patients. Ventilation/perfusion distribution measurement in six patients with pre-existing gas exchange limitations was not changed by sildenafil and treprostinil. Relevant side effects were not observed. Conclusion: The combination of sildenafil and inhaled treprostinil was well tolerated and induced additive, pulmonary selective vasodilatation in pulmonary hypertension patients. This could be of relevance also for long-term treatment of PAH and CTEPH patients. © 2008 Elsevier Ltd. All rights reserved.