Clinical Study to Assess the Long-term Safety and Tolerability of ACT 064992 in Patients With Symptomatic Pulmonary Arterial Hypertension

Inclusion Criteria:

• Signed informed consent prior to initiation of any study-mandated procedure.

• Patients with pulmonary arterial hypertension and having completed the event-drivenstudy, AC 055 302/SERAPHIN, or Patients who have experienced a clinical worsening ofPAH in AC 055 302/SERAPHIN and for whom a written approval to roll over into thisstudy has been obtained from the Sponsor.

• Women of childbearing potential must have a negative pre-treatment serum pregnancytest and must use a reliable method of contraception during study treatment and forat least 28 days after study treatment termination.

Exclusion Criteria:

• Any major violation of protocol AC 055 302/SERAPHIN.

• Pregnancy or breast-feeding.

• AST and/or ALT > 3 times the upper limit of the normal range.

• Any known factor or disease that might interfere with treatment compliance, studyconduct or interpretation of the results, such as drug or alcohol dependence orpsychiatric disease.

• Known hypersensitivity to ACT 064992 or any of the excipients.