Ambrisentan is an endothelin blocker approved for the treatment of pulmonary arterial hypertension. Patients with systemic sclerosis can have damage to their blood vessels, resulting in increased levels of endothelin in their bloodstream that then causes decreased blood flow to the digits. This can result in very painful digital ulcers. We hope to learn whether blocking the action of endothelin with ambrisentan will be helpful in the treatment and prevention of digital ulcers in patients with systemic sclerosis. This therapy is not approved for the treatment of systemic sclerosis, but this study will help us learn whether ambrisentan is safe and effective in the treatment and prevention of digital ulcers in patients with systemic sclerosis.