Extension of the Psychometric Validation Study ORCHESTRA in Patients With PAH

Inclusion Criteria:

1. Signed informed consent prior to any study-mandated procedure.

2. Patients with PAH who completed the ORCHESTRA study (AC-055-310) as scheduled

3. Women of childbearing potential (as defined below) must:

• Have a negative serum pregnancy test at Visit 1 (i.e., Visit 4 of study AC 055

310. and agree to perform monthly serum pregnancy tests.

• Agree to use two reliable methods of contraception in parallel, from Visit 1until 1 month after study drug discontinuation (see details below).
• A female is considered to have childbearing potential unless she meets atleast one of the following criteria:
• Previous bilateral salpingo and/or oophorectomy, or hysterectomy.
• Premature ovarian failure confirmed by a specialist.
• Pre-pubescence, XY genotype, Turner syndrome, uterine agenesis.
• Postmenopausal, defined as 12 consecutive months with no menseswithout an alternative medical cause.
• Of the two contraceptive methods that must be used, one must be from Group 1, and one must be from Group 2, defined as follows:
• Group 1: Oral, implantable, transdermal or injectable hormonalcontraceptives, intrauterine devices, female sterilization (tuballigation or non-surgical sterilization, e.g., permanent contraceptionwith Essure procedure), or partner's sterilization (vasectomy). If ahormonal contraceptive is chosen from this group, it must be takenfor at least one month prior to enrollment. Alternatively, if theEssure procedure is chosen as a contraceptive method, ahysterosalpingogram must have been performed to confirm correctlocation of the microinserts and tubal occlusion (as permanufacturer's recommendations).
• Group 2: Female or male condoms, diaphragm or cervical cap, any ofthem in combination with a spermicide.
• Sexual abstinence, rhythm methods, or contraception by the partner aloneare not considered as acceptable methods of contraception for this study.

Exclusion Criteria:

1. Patients who prematurely discontinued study drug in study AC-055-310.

2. Females who are lactating or pregnant (positive Visit 1 pregnancy test) or plan tobecome pregnant during the study.

3. AST and/or ALT more than 3 X ULN.