FUTURE 3 Study Extension

Inclusion Criteria: 1. Patients who completed the FUTURE 3 core study (AC-052-373) or prematurely discontinued due to PAH-progression, if bosentan was not permanently discontinued 2. Patients who tolerated bosentan pediatric formulation and for whom bosentan is considered beneficial at the end of the FUTURE 3 core study (AC-052-373) 3. Signed informed consent by the parents or the legal representatives prior to any study-mandated procedure. Exclusion Criteria: 1. Known intolerance or hypersensitivity to bosentan or any of the excipients of the dispersible bosentan tablet 2. Any clinically significant laboratory abnormality that precludes continuation of bosentan therapy 3. Pregnancy 4. AST and/or ALT values \> 3 times the upper limit of normal range (ULN) 5. Moderate to severe hepatic impairment, i.e., Child-Pugh Class B or C 6. Premature and permanent study drug discontinuation during the FUTURE 3 core study (AC-052-373) 7. Any major violation of the FUTURE 3 core study (AC-052-373) protocol.