The aim of the trial is to study the long-term safety of macitentan and to provide continued treatment with macitentan to patients with pulmonary arterial hypertension (PAH) and Chronic thromboembolic pulmonary hypertension (CTEPH) who were previously treated with macitentan in clinical studies.

The purpose of this study is to provide continued treatment with macitentan to subjects with PAH or CTEPH who participated in "parent studies" and to continue to accrue long-term safety data. The design of this study is widely used in clinical programs to give participants in a clinical study access to an effective study treatment beyond completion of the parent study. This is considered the best option to collect long-term safety and tolerability information of macitentan 10 mg and survival status of participants with PAH and CTEPH. "Parent study/studies" refer to a number of clinical studies with macitentan that are conducted in different clinical classification of PAH and CTEPH (NCT00667823, NCT02112487, NCT02310672, NCT02968901, NCT02558231, NCT02382016, NCT02060721) and may be completed before the participants have access to commercial macitentan in their country of residence. The "parent studies" are fully or partially running in countries where no access to commercial macitentan is expected in the near future.

Inclusion Criteria:

1. Signed informed consent to take part in the study before any study mandated procedure.
2. Participants from one of the parent studies and: a) the sponsor has decided to terminate the parent study in that country and b) the participant has completed the end of treatment (EOT) Visit of the parent study
3. Women of childbearing potential are able to take part in the study if the following applies: a) Urine pregnancy test is negative at Enrollment; b) Agreement to perform monthly urine or serum pregnancy tests during the study and up to at least 30 days after the study treatment discontinuation; and c) Agreement to adhere to the planned contraception scheme from Enrollment up to at least 30 days after study treatment discontinuation

Exclusion Criteria:

1. Hemoglobin less than 80 gram per liter (g/L)
2. Serum Aspartate aminotransferase (AST) and/or alanine aminotransferases (ALT) more than three times the upper limit of normal range
3. Known and documented history of severe hepatic impairment that is Child-Pugh Class C.
4. Pregnant, planning to become pregnant, or breastfeeding
5. Known hypersensitivity to macitentan, its excipients, or drugs of the same class
6. Planned or current treatment with another investigational treatment up to 3 months prior to Enrollment
7. Any known factor or disease that may interfere with treatment compliance, study conduct, or interpretation of the results, such as drug or alcohol dependence or psychiatric disease
8. Treatment with a strong CYP3A4 inhibitor (e.g., ketoconazole, itraconazole, voriconazole, clarithromycin, telithromycin, nefazodone, ritonavir, and saquinavir)