Background Iloprost has been used to test acute pulmonary vasoreactivity in idiopathic pulmonary arterial hypertension (PAH).We aimed to investigate the acute hemodynamic and oxygenation responses and tolerability to 20 μg aerosolized Iloprost in Chinese patients with pulmonary hypertension.Methods Between March 2005 and May 2010,212 pulmonary hypertension patients inhaled a single dose of 20 μg Iloprost over 10-15 minutes for vasoreactivity testing.The acute hemodynamic and oxygenation responses and adverse events were recorded.Results lioprost decreased total pulmonary resistance ((1747±918) dyn.s.cm-5 vs.(1581±937) dyn.s.cm-5,P ＜0.001),increased stroke volume ((45.0±22.1) ml vs.(47.0±24.2) ml,P=0.002),and cardiac output ((3.7±1.7) L/ml vs.(3.9±1.9)L/min,P=0.009).Heart rate and systemic vascular resistance remained stable during inhalation.However,systemic arterial blood oxygen saturation fell slightly ((91.0±6.8)％ vs.(90.3±6.7)％,P=0.002).Pulmonary and systemic arterial blood pressures declined within 1-3 minutes after inhalation initiation and reached their lowest levels within 10-15 minutes.Idiopathic PAH responded more favorably than pulmonary hypertension due to other causes (P≤0.001) and patients with less severe pulmonary hypertension have better responses to Iloprost.No adverse events requiring medical care or leading to termination of inhalation occurred.Conclusions Inhalation of 20 μg Iloprost showed potent and selective pulmonary hemodynamic effects and was well tolerated in the Chinese pulmonary hypertension patients.Patients with idiopathic PAH and less severe pulmonary hypertension responded more favorably to inhalation of Iloprost.