• Participant must sign an informed consent form (ICF) (or their legally designated representative must sign) indicating that participant understands the purpose of, and procedures required for, the study and is willing to participate in the study

• Participant treated with oral macitentan or selexipag or fixed dose combination (FDC) of macitentan 10 milligrams (mg) and tadalafil 40 mg at the end of a sponsor parent study and: a) the indication of the parent study is included in the intervention-specific appendices (ISA) (pulmonary arterial hypertension \[PAH\]; b) participant has completed the parent study; c) no alternative means of access to study intervention (or equivalent approved therapy) have been identified; d) participant may continue to benefit from treatment with the study intervention; e) Participant is at least 18 years old for macitentan/tadalafil FDC, and at least 2 years old for macitentan or selexipag

• A female participant of childbearing potential must: a) have a negative urine or serum pregnancy test prior to first intake of study intervention; b) agree to perform monthly urine pregnancy test up to the end of the safety follow-up period; c) If heterosexually active, agree to follow contraceptive methods until 30 days after the last intake of the study intervention. For pediatric female participants: It is the responsibility of the investigator to ensure appropriate counselling, including consultation with a specialist (if needed), to the participant and/or parent(s)/ legally designated representative (LDR)(s) on the acceptable method of contraception