Safety and Efficacy of BIA 5-1058 in PAH

This is an extension study with Pulmonary Arterial Hypertension (PAH) patients who are under treatment with zamicastat as adjunctive therapy in the study BIA-51058-201. For patients participating in this extension study, visit "Maintenance Period Visit 3" (MPV3) of the study BIA-51058-201 will also be the first visit (V1) of this extension study (BIA-51058-202). Their treatment with zamicastat will be continued at their individual highest tolerated dose (HTD) for an additional 12 weeks (50 mg, 100 mg, 150 mg or 200 mg). Further visits will be performed 20 ±3 days (V2, telephone), 41 ±3 days (V3, on-site), 62 ±3 days (V4, telephone) and 83 ±3 days (V5, on-site) after V1. At V5, patients will have the opportunity to continue treatment with zamicastat in a compassionate use program. Patients who will not participate in this compassionate use program will come to the following follow-up visit(s): * Follow-up (FU) down-titration (telephone, 14 ±2 days after V5); only applicable in patients taking 150 mg or 200 mg zamicastat * FU visit (on-site, 14 ±2 days after last investigational medicinal product (IMP) intake). The data and safety monitoring board (DSMB) will periodically review the safety data and will issue a recommendation if the study can be continued as planned.