GSK2586881, a purified intravenous (IV) formulation of soluble recombinant human Angiotensin Converting Enzyme (rhACE2) is being investigated as a treatment for PAH. This GlaxoSmithKline (GSK) study will evaluate the safety, tolerability, pharmacokinetics (PK) and pharmacodynamics (PD) of GSK2586881 in subjects with PAH. This open-label, dose-escalation study will comprise of 4 separate groups based on the planned dose range, and subjects in each group will be administered a single dose of GSK2586881 ranging between 0.2, 0.4, 0.8, or 1.2 milligram per kilogram (mg/kg) via IV route. Dose escalation will occur after 4 subjects have been dosed per cohort and review of safety, tolerability, PK and hemodynamic data up to 24 hours post dose has taken place. A maximum of 27 subjects will be included in the study and the total duration of the study will be up to a maximum of 59 days.