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-driven
study, AC 055 302/SERAPHIN, or Patients who have experienced a clinical worsening of
PAH in AC 055 302/SERAPHIN and for whom a written approval to roll over into this
study has been obtained from the Sponsor.

- Women of childbearing potential must have a negative pre-treatment serum pregnancy
test and must use a reliable method of contraception during study treatment and for at
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, study
conduct or interpretation of the results, such as drug or alcohol dependence or
psychiatric disease.

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