The primary purpose of this study is to investigate the rate and routes (urine and feces) of elimination of ACT-132577, and the mass balance in urine and feces

Inclusion Criteria:

• Signed informed consent in a language understandable to the subject prior to any study-mandated procedure;
• Healthy male subjects aged between 45 and 65 years (inclusive) at screening;
• Body mass index of 18.0 to 28.0 kg/m2 (inclusive) at screening;
• Healthy on the basis of physical examination, cardiovascular assessments and laboratory tests.

Exclusion Criteria:

• Values of hepatic aminotransferase (alanine aminotransferase and/or aspartate aminotransferase) > 3 × upper limit of normal range at screening;
• Hemoglobin < 100 g/L at screening;
• Known hypersensitivity to ACT-132577 or drugs of the same class, or any excipient of the ACT-132577 drug formulation;
• Known hypersensitivity or allergy to natural rubber latex;
• Previous exposure to ACT-132577;
• Treatment with another investigational drug within 3 months prior to screening or participation in more than 4 investigational drug studies within 1 year prior to screening;
• Any circumstances or conditions, which, in the opinion of the investigator, may affect full participation in the study or compliance with the protocol;
• A radiation burden of > 0.1 milliSievert (mSv) and ≤ 1.0 mSv in the period of 1 year prior to screening; a radiation burden of ≥ 1.1 mSv and ≤ 2.0 mSv in the period of 2 years prior to screening, etc. (add 1 year per 1 mSv).