The purpose of this study is to examine the potential of carbon monoxide (CO) to decrease elevated blood pressure in the pulmonary artery. This symptom is seen in patients with pulmonary arterial hypertension, a rare disease that causes fatigue, dizziness, and shortness of breath because the blood vessels that supply the lungs narrow, forcing the heart to work harder to push blood through. Previous studies in the laboratory have shown that carbon monoxide has promise in treating these symptoms.