This study is being conducted to see if PRX-08066 can lower pulmonary artery pressures in patients with pulmonary hypertension associated with chronic obstructive pulmonary disease.

Inclusion Criteria:

1. 25 to 79 years old.
2. Provide voluntary written informed consent to participate.
3. Smoking history of at least 10 pack years (1 pack of cigarettes per day for 10 years).
4. Diagnosis of chronic obstructive pulmonary disease.
5. Become short of breath with physical activity.
6. Elevated systolic pulmonary artery pressures.
7. Not pregnant, nursing, or planning a pregnancy.

Exclusion Criteria:

1. Left ventricular ejection fraction <30%.
2. Heart attack or stroke within the last 6 months.
3. History of lung resection surgery.
4. Use of supplemental oxygen >20 hours/day.
5. Blood donation or significant blood loss within the last 56 days.
6. Plasma donation within the last 14 days.
7. Use of any drugs for another research study within the last 30 days.
8. Use of vasodilators, long acting nitrates, prostacyclin analogs, endothelin antagonists, or phosphodiesterase inhibitor drugs within the last 14 days.
9. Positive blood screen Hepatitis B surface antigen (HBsAg) or Hepatitis C Antibody.
10. Major surgery within the last 28 days.
11. Any other medical condition that may jeopardize the safety of the subject, the validity of the study results, or interfere with the completion of the study according to the protocol.