Background Pulmonary arterial hypertension (PAH) is the commonest complication of left-to-right shunt congenitalheart disease (CHD).Detection of pulmonary vascular reactivity is important for the evaluation of patient with PAH.This study aimed to investigate the acute hemodynamie responses to iloprost in patients with idiopathic PAH (IPAH) and PAH associated with systemic-to-pulmonary shunt CHD (PAH-CHD).