Both macitentan and riociguat are indicated in the treatment of pulmonary arterial hypertension (PAH) and may be administered concomitantly. The primary objective of this study is to evaluate the effect of macitentan administered for 11 days on the pharmacokinetics (PK) (i.e., amount and time of presence in the blood of riociguat) of a single dose of riociguat in healthy male subjects.

Key Inclusion Criteria:

• Male subjects aged between 18 and 45 years (inclusive) at screening who signed informed consent prior to any study-mandated procedure;
• Healthy on the basis of physical examination, cardiac evaluations (12-lead ECG) and laboratory tests performed at screening;
• Body mass index of 18 to 30 Kg/m2 (inclusive) at screening;
• Systolic blood pressure 100-145 mmHg, diastolic blood pressure 50-90 mmHg, and pulse rate 50-90 beats per minute (inclusive).

Key Exclusion Criteria:

• Known allergic reactions or hypersensitivity to macitentan, riociguat, any drug of the same classes, or any of their excipients;
• Any contraindication for riociguat treatment;
• Known hypersensitivity or allergy to natural rubber latex;
• Previous history of fainting, collapse, syncope, orthostatic hypotension, or vasovagal reactions;
• History or clinical evidence of any disease and/or existence of any surgical or medical condition, which might interfere with the absorption, distribution, metabolism, or excretion of the study treatments;
• Previous treatment with any prescribed medications (including vaccines) or over the counter (OTC) medications (including herbal medicines such as St John's Wort, homeopathic preparations, vitamins, and minerals) within 3 weeks prior to first study treatment administration;
• Any circumstances or conditions, which, in the opinion of the investigator, may affect full participation in the study or compliance with the protocol.

Other protocol defined inclusion and exclusion criteria may apply.