Vasoconstrictive signaling via endothelin receptors is not limited to primary pulmonary
arterial hypertension, but has also been documented in secondary pulmonary hypertension due
to congestive heart failure, including cardiac valve disease. The investigators aim to
examine the clinical and physiologic effects of bosentan therapy in patients with secondary
pulmonary hypertension due to severe, inoperable cardiac valve disease, using a
single-center, prospective, open-label, non-randomized study of oral bosentan in outpatients
with severe mitral stenosis due to childhood rheumatoid fever. Primary end-point will be
exercise capacity at six months determined by six-minute walking distance and cardiopulmonary
exercise testing. Secondary end-points will be symptomatic relief, echocardiographic left
ventricular function and pulmonary pressure, serum pro-brain natriuretic peptide, and adverse
events at six months.