A Study of Ranolazine Acute Administration and Short Term Administration in Pulmonary Arterial Hypertension

The purpose of this study is to assess the safety of ranolazine in people with pulmonary arterial hypertension (PAH) and who are receiving 1 or more background PAH therapies: ambrisentan, sildenafil,tadalafil, epoprostenol, treprostinil (IV, SC, inhaled), or iloprost. The primary objective is: * To estimate the effect of ranolazine administration on acute hemodynamics. * To assess safety of ranolazine acutely over 6 hrs in the catheterization lab and after 12 weeks of therapy * To assess changes in right ventricular function after 12 weeks of therapy.