Acute myocardial infarction is an important cause of morbidity. This study aimed to investigate the effects of the administration of potassium chloride (KCl) on reperfusion-induced injuries in a rat model of myocardial ischemia/reperfusion. Thirty-six male Wistar rats, weighing 200 to 250 g, were randomly assigned to 3 experimental groups: control, K1 (10 µg/kg of KCl), and K2 (20 µg/kg of KCl). Twenty minutes before ischemia, a single dose of 10 and 20 µg/kg of KCl was intraperitoneally administered in the K1 and K2 groups, respectively. The coronary artery was occluded for 30 minutes (ischemia); thereafter, it was opened for 60 minutes (reperfusion) to measure hemodynamic parameters and ventricular arrhythmias. Blood sampling was performed after the reperfusion period to determine the serum levels of lactate dehydrogenase, troponin I, creatine kinase (CK)-MB, malondialdehyde, and pro-oxidant-antioxidant balance. Serological parameters significantly decreased in the potassium groups compared with the control group. In particular, the decline was more pronounced for the serum levels of lactate dehydrogenase (1180.25±69.48 vs 1556.67±77.02 U/L; P=0.011), troponin I (21.98±0.61 vs 28.76±1.65 ng/mL; P=0.020), and pro-oxidant-antioxidant balance (15.51±0.72 vs 20.63±1.42 HK; P=0.041) in the K2 group compared with the K1 group. Moreover, the administration of 20 µg/kg of KCl significantly decreased the incidence of ventricular tachycardias and fibrillations compared with the control group (P=0.002). Additionally, no considerable differences were observed between the control group and the groups with 10 µg/kg and 20 µg/kg of KCl regarding the number of ventricular ectopic beats. : The administration of KCl before ischemia could reduce ventricular arrhythmias and reperfusion-induced injuries by reducing oxidative stress.