A rapidly growing body of data supports the concept of in situ regulation of vascular tone: the ability of vasoactive substances to regulate vascular tone at their site of production within the wall of the vasculature. Sufficient data exist to suggest that ineffective production or response to endothelium-dependent vasodilator substances, or excessive production or responsiveness to endothelium-dependent vasoconstrictor substances may play an important role in cardiovascular disorders such as hypertension, coronary artery spasm, restenosis following coronary angioplasty, and congestive heart failure. The present review summarizes data which support the concept that endothelin, a potent vasoconstrictor produced by the endothelium, may play a role in the excessive vasoconstriction of heart failure. Increased circulating plasma endothelin may be particularly relevant to the range of pulmonary vasoconstriction encountered in congestive heart failure, with a correlation revealing that the greatest increase of plasma endothelin occurs in patients with marked pulmonary hypertension within the congestive heart failure patients studied. © 1992 The European Society of Cardiology.