Anastrozole in Patients With Pulmonary Arterial Hypertension

Inclusion Criteria: * Previous documentation of mean pulmonary artery pressure \> 25 mm Hg with a pulmonary capillary wedge pressure (or left ventricular end-diastolic pressure) \< 16 mm Hg and PVR \> 3 WU at any time before study entry. * Diagnosis of PAH which is idiopathic, heritable, drug- or toxin-induced, or associated with connective tissue disease, congenital heart disease, portal hypertension, or HIV infection. * Most recent pulmonary function tests with FEV1/FVC \>50% AND either a) total lung capacity \> 70% predicted or b) total lung capacity between 60% and 70% predicted with no more than mild interstitial lung disease on computerized tomography scan of the chest * Ability to perform six minute walk testing without limitations in musculoskeletal function or coordination. * If female, post-menopausal state, defined as: * \> 50 years old AND * a) have not menstruated during the preceding 12 months OR * b) have follicle-stimulating hormone (FSH) levels (\> 40 IU/L) OR * \< 50 years and FSH (\> 40 IU/L) OR * having had a bilateral oophorectomy * Informed consent Exclusion Criteria: * Treatment with estrogen or anti-hormone therapy (tamoxifen, fulvestrant, etc.) * WHO Class IV functional status * History of breast cancer * Clinically significant untreated sleep apnea * Left-sided valvular disease (more than moderate mitral valve stenosis or insufficiency or aortic stenosis or insufficiency), pulmonary artery or valve stenosis, or ejection fraction \< 45% on echocardiography * Initiation of PAH therapy (prostacyclin analogues, endothelin-1 receptor antagonists, phosphodiesterase-5 inhibitors) within three months of enrollment; the dose must be stable for at least 3 months prior to Baseline Visit * Hormone therapy * Hospitalized or acutely ill * Renal failure (creatinine \> 2.0) * Child-Pugh Class C cirrhosis * Current or recent (\< 6 months) chronic heavy alcohol consumption * Current use of another investigational drug (non-FDA approved) for PAH * Enrollment in a clinical trial within one month of screening * Age \< 18