Endothelin (ET) is a 21-amino acid peptide that is a critical component of disease progression in pulmonary arterial hypertension (PAH), a devastating and rapidly progressive condition that leads to right ventricular strain and dysfunction. ET has both acute and chronic deleterious effects that are mediated by two receptors—ET
A and ET
B. When treating patients with PAH, it is critical to block both receptors in order to achieve comprehensive benefits.