Experiments were performed in rats which had been pretreated with amiodarone 50 mg kg-1 day-1 p.o. for 4 weeks. In anaesthetized animals subject to 25 min of coronary artery occlusion, the rats which had received amiodarone had fewer ischaemia-induced ventricular premature beats than the controls (381 ± 106 compared with 815 ± 215, P = 0.070). The duration of arrhythmias induced by reperfusion following 5 min of ischaemia was also less in the rats which had received amiodarone than in the controls (43.8 ± 6.8 and 16.0 ± 3.1 s respectively). Pretreatment of rats with amiodarone reduced the maximum driving frequency of both isolated left atria and papillary muscles. There were no differences between the responses to α- or β-adrenoceptor agonists or to calcium in papillary muscle preparations from amiodarone-pretrcated and control rats. These results suggest that the antiarrhythmic activity of chronic amiodarone seen in the present study does not depend on changes in ventricular adrenoceptor responsiveness.