ET-1 is a potent vasoconstrictor. In pulmonary arterial vessels the ETA receptor is the predominant receptor (ratio of ETA to ET B = 9:1), which is responsible for vasoconstriction and remodeling of the pulmonal vasculature. In heart failure the ETA receptor is upregulated. Elevated plasma ET-1 levels correlate with pulmonary artery pressure (PAP), pulmonary vascular resistance (PVR) and inversely with peak exercise capacity.