Connexin 43 (Cx43) is the most prominent connexin in the mammalian ventricular myocardium and forms gap junctions that are essential for normal conduction of action potential. Carvedilol, a nonselective beta-blocker, is widely used to prevent ventricular arrhythmias after myocardial infarction (MI). Here, we examined the effect of carvedilol on the expression of Cx43 protein and ventricular fibrillation threshold (VFT) using a rat MI model. VFT is defined as the lowest voltage, at which ventricular fibrillation is induced by electrical stimulation. Adult male Wister rats were divided into sham-operated group (n = 20) and MI groups treated with intragastric administration of saline (control, n = 30) or carvedilol (2.5 mg/kg, n = 30) twice a day for 7 days immediately after ligation of the left coronary artery. Compared with sham group (100%), total Cx43 protein and phosphorylated Cx43 protein were decreased in the MI rats to 60 +/- 21% and 52 +/- 19% (both P < 0.05), respectively. Treatment with carvedilol prevented the MI-induced decrease in total and phosphorylated Cx43 levels (91 +/- 17% and 80 +/- 20%, both P < 0.05), respectively, which were similar to the levels of sham animals. Moreover, the MI rats exhibited a marked decrease in VFT compared with the sham group (7.2 +/- 1.30 vs. 13.0 +/- 2.12 V, P < 0.05), but the decrease was abolished by carvedilol (11.0 +/- 2.65 V). In conclusion, carvedilol might prevent the ischemia-induced ventricular arrhythmias by restoring Cx43 protein and VFT to the basal levels.