OBJECTIVE To investigate the potential differential effects of selective endothelin (ET) A and dual ET-A/B receptor blockade in patients with chronic heart failure. METHODS Nine patients with chronic heart failure (New York Heart Association class II-III) each received intravenous infusions of BQ-123 alone (selective ET-A blockade) and combined BQ-123 and BQ-788 (dual ET-A/B blockade) in a randomised, placebo controlled, three way crossover study. RESULTS Selective ET-A blockade increased cardiac output (maximum mean (SEM) 33 (12)%, p < 0.001) and reduced mean arterial pressure (maximum -13 (4)%, p < 0.001) and systemic vascular resistance (maximum -26 (8)%, p < 0.001), without changing heart rate (p = 0.38). Dual ET-A/B blockade significantly reduced the changes in all these haemodynamic variables compared with selective ET-A blockade (p < 0.05). Selective ET-A blockade reduced pulmonary artery pressure (maximum 25 (7)%, p = 0.01) and pulmonary vascular resistance (maximum 72 (39)%, p < 0.001). However, there was no difference between these effects and those seen with dual ET-A/B blockade. Unlike selective ET-A blockade, dual ET-A/B blockade increased plasma ET-1 concentrations (by 47 (4)% with low dose and 61 (8)% with high dose, both p < 0.05). CONCLUSIONS While there appeared to be similar reductions in pulmonary pressures with selective ET-A and dual ET-A/B blockade, selective ET-A blockade caused greater systemic vasodilatation and did not affect ET-1 clearance. In conclusion, there are significant haemodynamic differences between selective ET-A and dual ET-A/B blockade, which may determine responses in individual patients.