Selexipag (ACT-293987) in Pulmonary Arterial Hypertension

Inclusion Criteria: * Male and female patients 18-75 years old, with symptomatic PAH * PAH belonging to the following subgroups of the updated Dana Point Clinical Classification Group 1 (Idiopathic, or Heritable, or Drug or toxin induced, or Associated (APAH) with Connective tissue disease, Congenital heart disease with simple systemic-to-pulmonary shunt at least 1 year after surgical repair, or HIV infection) * Documented hemodynamic diagnosis of PAH by right heart catheterization, performed at any time prior to Screening * Six minute walk distance (6MWD) between 50 and 450 m at Screening within 2 weeks prior to the Baseline Visit * Signed informed consent Exclusion Criteria: * Patients with pulmonary hypertension (PH) in the Updated Dana Point Classification Groups 2-5, and PAH Group 1 subgroups that are not covered by the inclusion criteria * Patients who have received prostacyclin or its analogs within 1 month before Baseline Visit, or are scheduled to receive any of these compounds during the trial * Patients with moderate or severe obstructive lung disease * Patients with moderate or severe restrictive lung disease * Patients with moderate or severe hepatic impairment (Child-Pugh B and C) * Patients with documented left ventricular dysfunction * Patients with severe renal insufficiency * Patients with BMI \<18.5 Kg/m2 * Patients who are receiving or have been receiving any investigational drugs within 1 month before the Baseline Visit * Acute or chronic impairment (other than dyspnea), limiting the ability to comply with study requirements, in particular with 6MWT * Recently conducted or planned cardio-pulmonary rehabilitation program based on exercise training * Psychotic, addictive or other disorder limiting the ability to provide informed consent or to comply with study requirements * Life expectancy less than 12 months * Females who are lactating or pregnant or plan to become pregnant during the study * Known hypersensitivity to any of the excipients of the drug formulations