The effects of beta-adrenoceptor antagonists (dl-nebivolol, atenolol and propranolol) and of 1-nebivolol on cardiodynamics and mitochondrial oxidative phosphorylation were studied in the isolated working rabbit heart subjected to normothermic global ischemia, followed, in some cases, by reperfusion. The hearts were pretreated with the different drugs (0.32 mg/l) 30 min before the start of ischemia, dl-Nebivolol and propranolol provided protection for both cardiodynamic and mitochondrial functions, as did l-nebivolol, which lacks beta-adrenoceptor blocking properties, while atenolol failed to protect mechanical activity and cardiac mitochondria against the effects of ischemia and post-ischemic reperfusion. Catecholamine depletion with reserpine did not have a beneficial effect on the recovery of cardiodynamic and mitochondrial function during post-ischemic reperfusion. It is concluded that the beneficial effects of beta-blockers on the ischemic and reperfused myocardium can not be explained by a specific beta-blocking action alone.