<br>        Inclusion Criteria:<br><br>          1. PAH diagnosis confirmed with right heart catheterization (RHC):<br><br>               -  Idiopathic or heritable PAH, or<br><br>               -  Associated PAH persisting after complete repair of a congenital heart defect (PAH<br>                  has to be persistent for at least 6 months after surgery) or<br><br>               -  PAH-Congenital Heart Disease (PAH-CHD) associated with systemic-to-pulmonary<br>                  shunts (after global amendment dated 09 May 2012)<br><br>          2. World Health Organization functional Class (WHO FC) I, II or III<br><br>          3. Male or female = 3 months and < 12 years of age (maximum age at randomization is 11.5<br>             years)<br><br>          4. Body weight = 3.5 kg<br><br>          5. Peripheral oxygen saturation (SpO2) = 88% (at rest, on room air)<br><br>          6. Baseline PAH-therapy (Calcium channel blocker, bosentan, prostanoid, phosphodiesterase<br>             type-5 inhibitor) if present, has to be stable for at least 3 months prior to<br>             screening. During the study, all background treatments should remain stable<br><br>          7. Signed informed consent by the parents or legal representatives<br><br>        Exclusion Criteria:<br><br>          1. PAH etiologies other than listed above<br><br>          2. Non-stable disease status<br><br>          3. Need or plan to wean patient from intravenous epoprostenol or intravenous or inhaled<br>             iloprost<br><br>          4. Systolic blood pressure < 80% of the lower limit of normal range<br><br>          5. Aspartate aminotransferase and/or alanine aminotransferase values > 1.5 times the<br>             upper limit of normal range.<br><br>          6. Moderate to severe hepatic impairment, i.e., Child-Pugh Class B or C<br><br>          7. Hemoglobin and/or hematocrit levels < 75% of the lower limit of normal range.<br><br>          8. Known intolerance or hypersensitivity to bosentan or any of the excipients of the<br>             dispersible Tracleer tablet<br><br>          9. Treatment with forbidden medication within 2 weeks or at least 5 times the half-life<br>             prior to randomization, whichever is the longest:<br><br>               -  Glibenclamide (glyburide)<br><br>               -  Cyclosporin A<br><br>               -  Sirolimus<br><br>               -  Tacrolimus<br><br>               -  Fluconazole<br><br>               -  Rifampicin (rifampin)<br><br>               -  Ritonavir<br><br>               -  Co-administration of CYP2C9 inhibitors (e.g., amiodarone, voriconazole) and<br>                  moderate/strong CYP3A4 inhibitors (e.g., amprenavir, erythromycin, ketoconazole,<br>                  diltiazem, itraconazole)<br><br>               -  Endothelin receptor antagonists (ERAs) other than bosentan<br><br>         10. Treatment with another investigational drug within 1 month prior to randomization or<br>             planned treatment<br>      ;<br>        Inclusion Criteria:<br><br>          1. PAH diagnosis confirmed with right heart catheterization (RHC):<br><br>               -  Idiopathic or heritable PAH, or<br><br>               -  Associated PAH persisting after complete repair of a congenital heart defect (PAH<br>                  has to be persistent for at least 6 months after surgery) or<br><br>               -  PAH-Congenital Heart Disease (PAH-CHD) associated with systemic-to-pulmonary<br>                  shunts (after global amendment dated 09 May 2012)<br><br>          2. World Health Organization functional Class (WHO FC) I, II or III<br><br>          3. Male or female = 3 months and < 12 years of age (maximum age at randomization is 11.5<br>             years)<br><br>          4. Body weight = 3.5 kg<br><br>          5. Peripheral oxygen saturation (SpO2) = 88% (at rest, on room air)<br><br>          6. Baseline PAH-therapy (Calcium channel blocker, bosentan, prostanoid, phosphodiesterase<br>             type-5 inhibitor) if present, has to be stable for at least 3 months prior to<br>             screening. During the study, all background treatments should remain stable<br><br>          7. Signed informed consent by the parents or legal representatives<br><br>        Exclusion Criteria:<br><br>          1. PAH etiologies other than listed above<br><br>          2. Non-stable disease status<br><br>          3. Need or plan to wean patient from intravenous epoprostenol or intravenous or inhaled<br>             iloprost<br><br>          4. Systolic blood pressure < 80% of the lower limit of normal range<br><br>          5. Aspartate aminotransferase and/or alanine aminotransferase values > 1.5 times the<br>             upper limit of normal range.<br><br>          6. Moderate to severe hepatic impairment, i.e., Child-Pugh Class B or C<br><br>          7. Hemoglobin and/or hematocrit levels < 75% of the lower limit of normal range.<br><br>          8. Known intolerance or hypersensitivity to bosentan or any of the excipients of the<br>             dispersible Tracleer tablet<br><br>          9. Treatment with forbidden medication within 2 weeks or at least 5 times the half-life<br>             prior to randomization, whichever is the longest:<br><br>               -  Glibenclamide (glyburide)<br><br>               -  Cyclosporin A<br><br>               -  Sirolimus<br><br>               -  Tacrolimus<br><br>               -  Fluconazole<br><br>               -  Rifampicin (rifampin)<br><br>               -  Ritonavir<br><br>               -  Co-administration of CYP2C9 inhibitors (e.g., amiodarone, voriconazole) and<br>                  moderate/strong CYP3A4 inhibitors (e.g., amprenavir, erythromycin, ketoconazole,<br>                  diltiazem, itraconazole)<br><br>               -  Endothelin receptor antagonists (ERAs) other than bosentan<br><br>         10. Treatment with another investigational drug within 1 month prior to randomization or<br>             planned treatment<br>      ;<br>        Inclusion Criteria:<br><br>          1. PAH diagnosis confirmed with right heart catheterization (RHC):<br><br>               -  Idiopathic or heritable PAH, or<br><br>               -  Associated PAH persisting after complete repair of a congenital heart defect (PAH<br>                  has to be persistent for at least 6 months after surgery) or<br><br>               -  PAH-Congenital Heart Disease (PAH-CHD) associated with systemic-to-pulmonary<br>                  shunts (after global amendment dated 09 May 2012)<br><br>          2. World Health Organization functional Class (WHO FC) I, II or III<br><br>          3. Male or female = 3 months and < 12 years of age (maximum age at randomization is 11.5<br>             years)<br><br>          4. Body weight = 3.5 kg<br><br>          5. Peripheral oxygen saturation (SpO2) = 88% (at rest, on room air)<br><br>          6. Baseline PAH-therapy (Calcium channel blocker, bosentan, prostanoid, phosphodiesterase<br>             type-5 inhibitor) if present, has to be stable for at least 3 months prior to<br>             screening. During the study, all background treatments should remain stable<br><br>          7. Signed informed consent by the parents or legal representatives<br><br>        Exclusion Criteria:<br><br>          1. PAH etiologies other than listed above<br><br>          2. Non-stable disease status<br><br>          3. Need or plan to wean patient from intravenous epoprostenol or intravenous or inhaled<br>             iloprost<br><br>          4. Systolic blood pressure < 80% of the lower limit of normal range<br><br>          5. Aspartate aminotransferase and/or alanine aminotransferase values > 1.5 times the<br>             upper limit of normal range.<br><br>          6. Moderate to severe hepatic impairment, i.e., Child-Pugh Class B or C<br><br>          7. Hemoglobin and/or hematocrit levels < 75% of the lower limit of normal range.<br><br>          8. Known intolerance or hypersensitivity to bosentan or any of the excipients of the<br>             dispersible Tracleer tablet<br><br>          9. Treatment with forbidden medication within 2 weeks or at least 5 times the half-life<br>             prior to randomization, whichever is the longest:<br><br>               -  Glibenclamide (glyburide)<br><br>               -  Cyclosporin A<br><br>               -  Sirolimus<br><br>               -  Tacrolimus<br><br>               -  Fluconazole<br><br>               -  Rifampicin (rifampin)<br><br>               -  Ritonavir<br><br>               -  Co-administration of CYP2C9 inhibitors (e.g., amiodarone, voriconazole) and<br>                  moderate/strong CYP3A4 inhibitors (e.g., amprenavir, erythromycin, ketoconazole,<br>                  diltiazem, itraconazole)<br><br>               -  Endothelin receptor antagonists (ERAs) other than bosentan<br><br>         10. Treatment with another investigational drug within 1 month prior to randomization or<br>             planned treatment<br>      ;<br>        Inclusion Criteria:<br><br>          1. PAH diagnosis confirmed with right heart catheterization (RHC):<br><br>               -  Idiopathic or heritable PAH, or<br><br>               -  Associated PAH persisting after complete repair of a congenital heart defect (PAH<br>                  has to be persistent for at least 6 months after surgery) or<br><br>               -  PAH-Congenital Heart Disease (PAH-CHD) associated with systemic-to-pulmonary<br>                  shunts (after global amendment dated 09 May 2012)<br><br>          2. World Health Organization functional Class (WHO FC) I, II or III<br><br>          3. Male or female = 3 months and < 12 years of age (maximum age at randomization is 11.5<br>             years)<br><br>          4. Body weight = 3.5 kg<br><br>          5. Peripheral oxygen saturation (SpO2) = 88% (at rest, on room air)<br><br>          6. Baseline PAH-therapy (Calcium channel blocker, bosentan, prostanoid, phosphodiesterase<br>             type-5 inhibitor) if present, has to be stable for at least 3 months prior to<br>             screening. During the study, all background treatments should remain stable<br><br>          7. Signed informed consent by the parents or legal representatives<br><br>        Exclusion Criteria:<br><br>          1. PAH etiologies other than listed above<br><br>          2. Non-stable disease status<br><br>          3. Need or plan to wean patient from intravenous epoprostenol or intravenous or inhaled<br>             iloprost<br><br>          4. Systolic blood pressure < 80% of the lower limit of normal range<br><br>          5. Aspartate aminotransferase and/or alanine aminotransferase values > 1.5 times the<br>             upper limit of normal range.<br><br>          6. Moderate to severe hepatic impairment, i.e., Child-Pugh Class B or C<br><br>          7. Hemoglobin and/or hematocrit levels < 75% of the lower limit of normal range.<br><br>          8. Known intolerance or hypersensitivity to bosentan or any of the excipients of the<br>             dispersible Tracleer tablet<br><br>          9. Treatment with forbidden medication within 2 weeks or at least 5 times the half-life<br>             prior to randomization, whichever is the longest:<br><br>               -  Glibenclamide (glyburide)<br><br>               -  Cyclosporin A<br><br>               -  Sirolimus<br><br>               -  Tacrolimus<br><br>               -  Fluconazole<br><br>               -  Rifampicin (rifampin)<br><br>               -  Ritonavir<br><br>               -  Co-administration of CYP2C9 inhibitors (e.g., amiodarone, voriconazole) and<br>                  moderate/strong CYP3A4 inhibitors (e.g., amprenavir, erythromycin, ketoconazole,<br>                  diltiazem, itraconazole)<br><br>               -  Endothelin receptor antagonists (ERAs) other than bosentan<br><br>         10. Treatment with another investigational drug within 1 month prior to randomization or<br>             planned treatment<br>