Exercise Induced Pulmonary Hypertension in Systemic Sclerosis and Treatment With Ambrisentan

Inclusion Criteria: 1. Systemic Sclerosis diagnosed by the American College of Rheumatology consensus statement including any of the following: * Limited * Diffuse * Sine Scleroderma 2. Patients must be willing and able to undergo right heart catheterization with lower extremity cycle ergometry 3. Mean pulmonary artery pressure (mPAP) \> 30mmHg with exercise; PCWP ≤ 15mmHg on RHC at rest 4. Men and women, ages 18 years of age or older 5. Standard adjunctive medications will be allowed concurrently in this study at the discretion of the treating pulmonologist and rheumatologist, including digoxin, diuretics, anticoagulants (e.g. warfarin), stable immunosuppression or other anti-fibrotic therapy for at least one month prior to enrollment Exclusion Criteria: 1. Resting PAH (mPAP \> 25mmHg) on right heart catheterization 2. Other known causes of PAH including prior venous thromboembolism, HIV infection, chronic liver disease with portal hypertension, left ventricular systolic dysfunction (e.g. LVEF \< 40%), and congenital causes of PAH 3. Severe hepatic disease precluding the use of ambrisentan (AST/ALT ≥3x ULN). 4. Women who are pregnant or breastfeeding. 5. Concurrent therapy with a prostanoid or prostanoid analogue, PDE5 inhibitors, or enrolled in another active clinical study. 6. Use of any prostacyclin or endothelial receptor antagonist (ERA) within 30 days before study entry. 7. Bed or wheel chair bound or a baseline 6-Minute Walk distance (6MWD) less than 150 meters. 8. Childbearing capable women who are unwilling or unable to use an acceptable method to avoid pregnancy for the entire study period. 9. New York Heart Association (NYHA) Classification: Class IV 10. Renal dysfunction (serum creatinine \>2.5mg/dL). 11. Uncontrolled sleep apnea.