OBJECTIVE To elucidate the effect of selective endothelin ET(A)- and mixed ET(A/B)-receptor antagonists on endothelial vasomotor dysfunction in rats with heart failure after myocardial infarction (MI). METHODS Vasoreactivity and superoxide anion formation were determined in aortic rings from Wistar rats 12 weeks after extensive MI (>46% of left ventricle) compared to sham-operated animals. Rats were either treated with the selective ET(A)-receptor antagonist LU 135252 (30 mg/kg/day), the mixed ET(A/B)-receptor antagonist Bosentan (100 mg/kg/day) or placebo. RESULTS In MI rats, the concentration-response curve of the endothelium-dependent, nitric oxide-mediated relaxation induced by acetylcholine was significantly shifted to the right and the maximum relaxation was attenuated. Long-term treatment with both ET antagonists significantly improved acetylcholine-induced relaxation in MI rats. LU 135252 was more effective than Bosentan. Endothelium-independent relaxations induced by sodium nitroprusside as well as endothelin- and phenylephrine-induced contractions were similar in all groups of rats. Plasma renin activity and aortic superoxide formation, which were enhanced in rats with heart failure, were normalized by LU 135252, but not by Bosentan treatment. CONCLUSIONS Long-term treatment with ET-receptor antagonists improves endothelial vasomotor dysfunction in rats with chronic MI. This mechanism may essentially contribute to the beneficial effects of ET receptor blockade in heart failure.