Non-interventional Multi-center Study on Patients Under Routine Treatment of Pulmonary Arterial Hypertension (PAH) With Inhaled Iloprost Using I-Neb as a Device for Inhalation

Inclusion Criteria: * Adult patients (age ≥ 18years old), male or female * Diagnosis of Pulmonary Arterial Hypertension, Group I of the Dana Point Pulmonary Hypertension classification (Diagnosis made at the discretion of the attending investigator, including mPAP ≥ 25 mmHg at rest, as measured by right heart catheterization.) * The treating physician has chosen to initiate the treatment with inhaled iloprost with I-Neb device for the application, as described in the Summary of Product characteristics (SmPC). * WHO/NYHA functional class III * Willing to participate in the study (Informed Consent Sign) * Patients who received the first inhaled iloprost treatment with I-Neb from February 1st, 2013. Exclusion Criteria: * Any contraindication for the treatment with Ventavis as described in the Summary of Product characteristics (SmPC) * Patients are not to be enrolled if they were treated with inhaled iloprost with I-Neb or any other device for the application in the past, before the start of the observation period (February 1st, 2013)