Study the Safety and Effectiveness of Tadalafil on High Blood Pressure in the Blood Vessel Going From the Heart to the Lungs

An Extension Study to Evaluate the Long-Term Safety and Efficacy of the Phosphodiesterase Type 5 (PDE5) Inhibitor Tadalafil in the Treatment of Patients With Pulmonary Arterial Hypertension

Study to determine the long term safety of tadalafil in patients with increased blood pressure in the blood vessel that carries blood from the right heart to the lungs and to see if it will keep the disease from getting worse.

Inclusion Criteria:

• Must have participated and discontinued in the previous PAH placebo controlled study due to clinical worsening on placebo or tadalafil 2.5 mg, 10mg, or 20 mg
• Must have completed Week 16 of the previous PAH study and had either no clinical worsening or became clinically worse at the Week 16 visit on placebo or tadalafil 2.5 mg, 10mg, or 20 mg
• Females who have a negative urine pregnancy test and are willing to use 2 types of birth control
• Be 12 years or older (country specific regulations apply) with parental approval

Exclusion Criteria:

• Participated in the placebo controlled study and had clinical worsening on 40 mg tadalafil
• Have left-sided heart disease
• Have a musculoskeletal disorder that limits being able to get around
• Nitrate use
• Certain current systemic treatments