The purpose of this 8-week study is to compare the effects of switching from intravenous Flolan to intravenous Remodulin therapy. Remodulin (treprostinil sodium) is an approved therapy for pulmonary arterial hypertension (PAH). Unlike Flolan, Remodulin does not need to be mixed daily and is stable at room temperature, so there is no need for ice packs. In addition, Remodulin is changed every 48hrs, instead of every 12-24 (with ice packs) or every 8 hours (without ice packs) with Flolan. Flolan is given using a type of portable medication pump called the CADD Legacy infusion pump. In this study, Remodulin will be given using a smaller and lighter medication pump called the Crono Five infusion pump. This study will also assess the effect that changing to Remodulin will have on treatment satisfaction and patient quality of life.