The purpose of this study is to evaluate whether giving a drug called treprostinil earlier in a patient’s pulmonary arterial hypertension (PAH) diagnosis and then quickly increasing the dose will improve the patient’s PAH symptoms and function of the right ventricle (a chamber of the heart), as well as reverse right ventricular remodeling (changes in heart size and shape due to PAH). Two types of treprostinil will be used in this study: parenteral treprostinil and oral treprostinil. Both parenteral and oral treprostinil are approved by the U.S. Food and Drug Administration (FDA) for the treatment of PAH. Study procedures include completing quality of life questionnaires, physical exams, blood draws, electrocardiograms, cardiac magnetic resonance imaging, echocardiograms, 6-minute walk tests, and right heart catheterization (RHC, a procedure to measure heart pressure). A device called the CardioMEMS PA Sensor will be permanently implanted in the pulmonary artery during the RHC procedure. This device is approved by the U.S. Food and Drug Administration (FDA) for heart failure, but its use in PAH is investigational.