This multicenter, open label, single-arm study is aim at investigating the the efficacy and safety of china made ambrisentan in Chinese subjects with PAH.

Pulmonary arterial hypertension is a hemodynamic and pathophysiological state, which can cause progressive hyperplasia of pulmonary vascular walls and elevated pulmonary arterial pressure for various reasons. Ambrisentan is a selective endothelin-A (ETA) receptor antagonist with vasodilatory, antiproliferative and vascular remodeling effects at a dose of 5 mg or 10 mg once daily, oral. A number of international clinical studies have shown that ambrisentan can improve the hemodynamic parameters, WHO functional classification and exercise tolerance of PAH patients, and improve the survival rate. The domestic Ambrisentan tablet is produced by Jiangsu Hansoh Pharmaceutical Group Co., Ltd. under the trade name of "Pu Nuo An". It has been developed and completed according to the consistency evaluation standard after the bioequivalence test, and is currently listed in mainland China. In view of the low price of the domestic ambrisentan, in order to verify its efficacy and safety in the real world, this post-marketing multicenter clinical study was carried out.

Inclusion Criteria:

• Age ≥18 years old and ≤75 years old, regardless of gender;

• patients weighing ≥ 40 kg;

• Patients diagnosed with PAH in Group 1 of the WHO Updated Clinical Classification of Pulmonary Hypertension (WHO functional class II or III);

• 6 min walk test (6MWT), walking distance ≥ 50 m;

• Right heart catheterization performed within 6 months prior to screening and meeting the following hemodynamic criteria:

  1. mean pulmonary artery pressure ≥ 25 mm Hg；
  2. Pulmonary vascular resistance ≥ 240 dyn·s·cm-5;
  3. Pulmonary artery wedge pressure or left ventricular end-diastolic pressure ≤ 15 mmHg;

• Subject receiving calcium channel blocker (CCB) drugs, only those whose doses have been stabilized for more than 4 weeks at the time of screening are allowed to be included in the study;

• Pulmonary function testing performed within 6 months prior to screening and meeting the following criteria：

  1. Total lung capacity ≥ 60% of normal predicted value;
  2. Forced expiratory volume in one second (FEV1) ≥ 55% of normal expected value;

• Female subjects of childbearing potential must have a negative pregnancy test at the Screening Visit and Day 0;

• Females subjects of childbearing potential must use a medically acceptable method of contraception (eg, hormone therapy, IUD, barrier methods such as condoms or cervical caps) during the study;

• Sign written informed consent

Exclusion Criteria:

• Patients diagnosed with WHO updated PH clinical classification of group 2, 3, 4, 5;
• Endothelin receptor antagonist therapy (eg, bosentan) has been discontinued prior to enrollment due to safety or tolerability concerns (non-drug-induced liver function abnormalities);
• Serum alanine aminotransferase (ALT) or aspartate aminotransferase (AST) levels > 2 times ULN;
• Serum bilirubin level > 1.5 times ULN;
• severe hepatic insufficiency (Child-Pugh class C);
• severe renal insufficiency (creatinine clearance <30 mL/min);
• Hemoglobin concentration < 10 g/dL or hematocrit < 30%;
• Contraindications to treatment identified by laboratory tests, physical examination, medical history, or other investigations
• severe hypotension (diastolic < 50 mm Hg or systolic < 90 mm Hg);
• Clinically significant aortic or mitral valve disease, pericardial constriction, restrictive or congestive cardiomyopathy, fatal arrhythmias, LV ejection fraction < 45%, LV outflow tract obstruction, symptomatic coronary heart disease, spontaneously low blood pressure;
• A history of malignancy within 5 years prior to enrollment, except for basal cell carcinoma of the skin and carcinoma in situ of the cervix;
• Subject taking endothelin receptor antagonists such as ambrisentan, bosentan and macitentan within 4 weeks prior to enrollment;
• pregnant and lactating women;
• Subject deemed unsuitable for participation in this study by other investigators