The study will be conducted in patients who are enrolled in the German Ventavis patient support program Ventaplus which is executed for Bayer by the company Contra Care GmbH, Nürnberg. Patients who are enrolled in the program and repeatedly experienced extended inhalation times with Ventavis (Iloprost) 10 μg/mL which could possibly result in incomplete inhalations, are currently being switched to Ventavis (Iloprost) 20 μg/mL by their physician.