• Total exercise time on the exercise echocardiogram using the standard Bruce stress protocol. This will be determined after 16 weeks on the study medication.
  

• Changes in exercise-induced pulmonary pressures on the exercise echo; 6 minute walk distance, BNP level, ET-1 level, QOL (via SF-36 questionnaires) and other patient dyspnea questionnaires.
  

Pulmonary hypertension (PAH) is a common and usually fatal form of lung disease in systemic sclerosis (SSc). Multiple drugs have been approved for the treatment of Class III/IV PAH in scleroderma. Bosentan is an endothelin-1 antagonist which showed significant improvement in distance walked during 12 week clinical trials in PAH patients (7). Therapy for asymptomatic systemic sclerosis patients diagnosed incidentally with PAH (WHO Functional Class I) remains controversial. We hypothesize that asymptomatic or minimally symptomatic patients with systemic sclerosis and normal resting pulmonary artery pressures who demonstrate an abnormal rise in pulmonary artery systolic pressure with stress Doppler echocardiography testing represent a subset of patients who already have pulmonary vascular disease and who are at risk for the development of severe PAH. We further hypothesize that early identification and treatment of such patients may retard the progression of that disease.

Hypotheses:

1. Stress echocardiography identifies early pulmonary vascular disease by detecting exercise-induced pulmonary hypertension in patients with systemic sclerosis.
2. Treatment of exercise-induced PAH with Bosentan will lead to improved exercise endurance in patients with systemic sclerosis.

Subjects will be recruited from those patients who have had an abnormal exercise test as part of an earlier study, Exercise Echocardiograms in Scleroderma (IRB# 03-363).