Oral administration of 600 mg/day of carbamazepine to 14 arrhythmic chagasic patients with advanced myocardial damage and no signs of congestive heart failure did not alter the frequency of ventricular extrasystoles, but reduced the total number of supraventricular ectopic beats in 7/14 patients and the episodes of complex ventricular arrhythmias in up to 43% of patients. This assessment was made from 24 hour continuous Holter recording during the course of this double-blind, placebo controlled, randomized crossover study. Serum levels of carbamazepine were also determined and found within therapeutic limits. Six patients complained of minor side effects. One patient presented with iatrogenic complete AV block, another case had proarrhythmic effect and one patient had to be withdrawn from the study because of gastric irritation. No instance of contractile depression was observed. Accordingly, carbamazepine is a therapeutic alternative for treatment of symptomatic complex ventricular or supraventricular arrhythmias in chronic chagasic patients without evidence of conduction system involvement or with intolerance to other antiarrhythmic drugs.