Anaesthetically equipotent doses of lidocaine, bupivacaine and a new bupivacaine-like local anaesthetic agent, ropivacaine, were injected into the left anterior descending coronary artery of pentobarbital-anaesthetized pigs. The aim was to study the cardiotoxicity of ropivacaine in relation to the two other drugs. A random, crossover, dose response study design was used. The following doses of the drugs were adminstered: lidocaine (L): 1, 2, 4, 8, and 16 mg, bupivacaine (B): 0.25, 0.5, 1, 2, and 4 mg and ropivacine (R): 0.33, 0.66, 1.33, 2.66, 5.33 mg. Systemic haemodynamics, left ventricular dP/dT and a 12-lead electrocardiogram were recorded continuously during the study period. The drugs depressed cardiac contractility in relation to their local anaesthetic potency on the isolated nerve - 4 :3: 1 (B:R:L). The prolongation of the ECG QRS-interval was regarded as a measure of electrophysiologic toxicity. Comparable prolongation of the QRS-interval was recorded after 2 mg or bupivacaine, 4.5 mg of ropivacain, and 30 mg of lidocaine. Thus, the electrophysiological toxicity ratio was 15: 6.: 1 (B:R:L). Provided local anaesthetic potency data can be extrapolated from the isolated nerve preparation to regional anaesthesia in humans, ropivacine appears to provide a greater margin of safety than bupivaciane, if inadvertantly injected into the venous circulation.