The purpose of this study is to provide sildenafil therapy to subjects who have completed the A1481156 study for the treatment of Pulmonary Arterial Hypertension (PAH) in India and are judged by the Investigator to derive clinical benefit from continued treatment with sildenafil citrate. Sildenafil citrate will be supplied for the treatment of Pulmonary Arterial Hypertension (PAH) until the subject continues to derive benefits from the treatment. The treating physicians (and the sponsor) will be responsible for reporting serious adverse events.

Inclusion Criteria:

• Subjects who have completed study A1481156 and are judged by the Investigator to derive clinical benefit from continuous treatment with sildenafil citrate therapy.
• Subjects with pulmonary arterial hypertension (PAH ) being treated at a study site in India
• Subjects who are willing and able to comply with scheduled visits, treatment plan, and other study procedures

Exclusion Criteria:

• Pregnant or lactating female subjects.
• Current participation in other studies and during study participation, except for the A1481304 follow-up period.
• Other severe acute or chronic medical or psychiatric condition or laboratory abnormality that may increase the risk associated with study participation or investigational product administration and, in the judgment of the investigator, would make the subject inappropriate for entry into this study.