What is the most cardiotoxic local anesthetics drug?

Bupivacaine-answer: e (katzung, pp 426, brunton, pp 377) most local anesthetics can block na+ channels in cardiac muscle and thus they can depress automaticity and conduction. at very high doses they can also depress contractility, likely by blocking ca++ channels. bupivacaine is more cardiotoxic than most other local anesthetics, apparently because the drug dissociates much more slowly than other local anesthetics during diastole, so a significant fraction of na+ channels at physiological heart rates remains blocked with bupivacaine at the end of the diastole. bupivacaine induced cardiac toxicity is very difficult to treat and is enhanced by coexisting acidosis and hypoxemia. a, b, c, d) (see explanation above)