This is a multicentre, open label, single-arm study in approximately 20 adult patients (18 - 75 years old) designed to evaluate the Impact on lifestyle of a new thermo stable formulation of epoprostenol sodium in subjects with Pulmonary Arterial Hypertension (PAH). The co-primary objectives are 1) to describe the effect of the new thermo stable formulation of epoprostenol sodium on quality of life and 2) to determine the dose titration requirement in patients switching from the currently marketed FLOLAN (epoprostenol sodium) to the new thermo stable formulation. Secondary objectives include assessing the safety, tolerability and efficacy of the thermo stable formulation of epoprostenol sodium and the exploratory objective is to evaluate the effect of the new thermo stable formulation of epoprostenol sodium on haemodynamic parameters in a subset of subjects.