An association between cardiac arrhythmias and ethanol use has been observed for some time. The sympathetic nervous system presumably plays an important role in the manifestation of cardiovascular ethanol responses. Therefore, we investigated the effects of ethanol treatment on epinephrine-induced arrhythmias. Female Wistar rats received 10 vol% ethanol or 2.5% glucose (control group) in their drinking water for 45 days. In ether anesthetized animals of both groups epinephrine (10 micrograms/kg.min) was infused via a lateral tail vein. The threshold dose for arrhythmias after epinephrine infusion (mainly 2nd and 3rd degree AV-blocks) was reduced beginning 2 days after the start of the ethanol treatment and the incidence of AV-blocks during epinephrine infusion was increased. During the ethanol treatment the prohypertensive epinephrine effect was slightly increased. The reflex bradycardia was not changed after repeated epinephrine infusion by ethanol treatment, whereas it was nearly abolished in the control group. No blood ethanol could be detected during the time of epinephrine infusion (9-12 a.m.), but determinations at 11 p.m. yielded a concentration of 0.13 +/- 0.02 mg/g. The results show that the epinephrine-induced bradyarrhythmia threshold is reduced and the frequency of arrhythmic events is augmented in rats exposed to ethanol in the drinking fluid.