Functional and metabolic effects of bupivacaine and lignocaine in the rat heart-lung preparation. We have examined the effects of bupivacaine and lignocaine on myocardial metabolism in the rat isolated heart-lung preparation. Bupivacaine 1, 5 or 25 micrograms ml-1 or lignocaine 4, 20 or 100 micrograms ml-1 was administered 5 min after the start of perfusion. Both bupivacaine 25 micrograms ml-1 and lignocaine 100 micrograms ml-1 reduced heart rate significantly. Bupivacaine 25 micrograms ml-1 was associated with a higher incidence of arrhythmias than the other groups. Three hearts in the bupivacaine 25 micrograms ml-1 group (n = 8) and two hearts in the lignocaine 100 micrograms ml-1 group (n = 8) failed (zero cardiac output) at the end of the experiment. Although there were no significant differences in myocardial lactate and glycogen concentrations between groups, ATP content in the bupivacaine 25 micrograms ml-1 and lignocaine 100 micrograms ml-1 groups was significantly less than that in the control group. The results suggest that myocardial depression and subsequent metabolic deterioration occurred with both the high doses of local anaesthetics; these findings do not account for the apparent increased cardiotoxicity of bupivacaine. 