This is a multi-center, single-arm, prospective study to enroll patients diagnosed as pulmonary arterial hypertension. The expected study period will be 2 years. PAH patients, who met NHI criteria, to receive treprostinil subcutaneously/ intravenously, will be invited to join this study for observation. The dosage and administration schedule of study medication will be judged by investigators. If the eligibility criteria have been met and the subject have signed the informed consent, the subjects will be enrolled into this study. There will be 10 visits: Visit 1 (Screening visit, Week -2 \~ -1), Visit 2 (Week 1, initial of use treprostinil), Visit 3 to 9 (Week 13 to 85), Visit 10 (Week 97). The Day 1 in Week 1 should be the start day of treprostinil treatment. Subjects will be returned to the clinics every 3 months (i.e. 12 weeks) after Visit 2. The NT-proBNP level, WHO functional class, 6-minute walk distance, echocardiography, pulse oximetry, modified Borg Dyspnea Scale, SF-36 questionnaire, and dosage regimens of treprostinil (including dose adjustment) will be collected. For time to clinical worsening and death, it will be followed up during study period. All intercurrent events within 24 months will be recorded. Safety information, including vital signs, and physical exams will be checked. Adverse events of special interest (AESIs) will be reviewed every visit by using a predesignated AESI checklist.
