The Efficacy and Safety of Initial Triple Versus Initial Dual Oral Combination Therapy in Patients With Newly Diagnosed Pulmonary Arterial Hypertension

Inclusion Criteria: 1. Signed informed consent prior to any study-mandated procedure. 2. Male or female ≥ 18 and ≤ 75 years of age at screening. 3. Initial PAH diagnosis \< 6 months prior to enrollment. 4. RHC performed between Day -28 and Day 1, meeting all the following criteria: * Mean pulmonary artery pressure (mPAP) ≥ 25 mmHg. * Pulmonary artery wedge pressure or left ventricular end-diastolic pressure ≤ 15 mmHg. * PVR ≥ 480 dyn•sec/cm5 (≥ 6 Wood Units). * Negative vasoreactivity test mandatory in idiopathic, heritable, and drug/toxin induced PAH (at this or a previous RHC). 5. Symptomatic PAH belonging to one of the following subgroups: * Idiopathic. * Heritable. * Drug or toxin induced. * Associated with one of the following: connective tissue disease; HIV infection; congenital heart disease. 6. 6-minute walk distance (6MWD) ≥ 50 m at screening. 7. Women of childbearing potential must not be pregnant, must perform regular pregnancy tests, and use reliable contraception. Exclusion Criteria: 1. Any PAH-specific drug therapy at any time. 2. Cardio pulmonary rehabilitation program based on exercise (planned, or started ≤ 12 weeks prior to Day 1). 3. Body mass index (BMI) \> 40 kg/m2 at screening. 4. Presence of three or more of the following risk factors for heart failure with preserved ejection fraction at screening: * BMI \> 30 kg/m2. * Diabetes mellitus of any type. * Essential hypertension. * Coronary artery disease, i.e., any of the following: * History of stable angina or * More than 50% stenosis in a coronary artery (by coronary angiography) or * History of myocardial infarction or * History of or planned coronary artery bypass grafting and/or coronary artery stenting. 5. Acute myocardial infarction ≤ 12 weeks prior to screening. 6. Stroke ≤ 12 weeks prior to screening. 7. Known permanent atrial fibrillation. 8. SBP \< 90 mmHg at screening or Day 1. 9. Ongoing or planned treatment with organic nitrates and/or doxazosin. 10. Presence of one or more of the following signs of relevant lung disease at any time up to screening: * Diffusing capacity of the lung for carbon monoxide (DLCO) \< 40% of predicted (eligible only if no or mild interstitial lung disease on computed tomography). * Forced vital capacity (FVC) \< 60% of predicted. * Forced expiratory volume in one second (FEV1) \< 60% of predicted. 11. Known or suspected pulmonary veno-occlusive disease (PVOD). 12. Documented severe hepatic impairment (with or without cirrhosis) according to National Cancer Institute organ dysfunction working group criteria, defined as total bilirubin \> 3 × upper limit of the normal range (ULN) accompanied by aspartate aminotransferase (AST) \> ULN (assessed by central laboratory at screening); and/or Child-Pugh Class C. 13. Serum AST and/or alanine aminotransferase (ALT) \> 3 × ULN (assessed by central laboratory at screening). 14. Severe renal impairment (estimated creatinine clearance ≤ 30 mL/min/1.73 m2) assessed by central laboratory at screening. 15. Ongoing or planned dialysis. 16. Hemoglobin \< 100 g/L assessed by central laboratory at screening. 17. Known or suspected uncontrolled thyroid disease (hypo- or hyperthyroidism). 18. Loss of vision in one or both eyes because of non-arteritic ischemic optic neuropathy (NAION). 19. Treatment with strong inducers of cytochrome P450 3A4 (CYP3A4; e.g., carbamazepine, rifampin, rifampicin, rifabutin, rifapentin, phenobarbital, phenytoin, and St. John's wort) ≤ 28 days prior to Day 1. 20. Treatment with strong inhibitors of CYP3A4 (e.g., ketoconazole, itraconazole, voriconazole, clarithromycin, telithromycin, nefazodone, ritonavir, and saquinavir) and/or strong inhibitors of CYP2C8 (e.g., gemfibrozil) ≤ 28 days prior to Day 1. 21. Treatment with another investigational drug (planned, or taken ≤ 12 weeks prior to Day 1). 22. Hypersensitivity to any of the 3 study treatments or any excipient of their formulations. 23. Pregnancy, breastfeeding, or intention to become pregnant during the study. 24. Concomitant life-threatening disease with a life expectancy \< 12 months. 25. Alcohol abuse. 26. Any factor or condition likely to affect protocol compliance of the subject, as judged by the investigator.