The primary objective of this study is to monitor the long-term safety of ambrisentan in adult participants with pulmonary hypertension. The available ambrisentan doses for this study are 2.5, 5, or 10 mg administered orally once daily. Investigators will be able to adjust ambrisentan dose as clinically indicated. A minimum of 4 weeks between dose adjustments is required. Participants receiving other therapies for pulmonary hypertension that are not contraindicated for concomitant use with ambrisentan are permitted to enroll in this study and continue to receive such therapies. Participants enrolled in this study will receive treatment with ambrisentan until such time as the investigator or participant chooses to stop ambrisentan treatment, ambrisentan becomes commercially available, or the sponsor stops the study.

Key Inclusion Criteria:

• Men and women with pulmonary hypertension who are discontinuing a clinical study of ambrisentan due to study closure by the sponsor. Eligible participants are those participating in countries where ambrisentan is not yet commercially available. Participants participating in countries where ambrisentan is commercially available may be eligible if they do not qualify for treatment per the current prescribing information of that country.

Key Exclusion Criteria:

• Participants who have discontinued an ambrisentan clinical study for any other reason than sponsor-initiated study closure are not eligible.

Note: Other protocol defined Inclusion/Exclusion criteria may apply.