FUTURE 3 Study Extension

Inclusion Criteria:

1. Patients who completed the FUTURE 3 core study (AC-052-373) or prematurelydiscontinued due to PAH-progression, if bosentan was not permanently discontinued

2. Patients who tolerated bosentan pediatric formulation and for whom bosentan isconsidered 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 anystudy-mandated procedure.

Exclusion Criteria:

1. Known intolerance or hypersensitivity to bosentan or any of the excipients of thedispersible bosentan tablet

2. Any clinically significant laboratory abnormality that precludes continuation ofbosentan 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.