Background: Coronary artery bypass grafting (CABG) surgery is a treatment option for coronary artery diseases. Cardiac arrhythmias during CABG surgery can lead to serious complications. Potassium ion concentration is a factor involved in such arrhythmias. Objectives: This study aimed to investigate the relationship between potassium concentration and cardiac arrhythmias in CABG surgery. Methods: This descriptive cross-sectional study was performed on 60 patients with the American Society of Anesthesiologists class I, II, and III undergoing CABG surgery at Golestan Hospital, Ahvaz, Iran. All patients underwent general anesthesia, and ventilator control was achieved by mechanical ventilation. The on-pump method was used for CABG. Potassium levels were measured at several time points during surgery. All cardiac arrhythmias were recorded. Mean arterial pressure (MAP), serum level of potassium, blood sugar, blood urea nitrogen (BUN), creatinine, calcium, magnesium, hemoglobin (Hb), and sodium were also recorded. Results: The mean age of the patients was 60.87 ± 7.35 years, and 45% of the subjects were female. Moreover, there was no statistically significant difference between the patients. There was a significant relationship between the changes in MAP, potassium, blood sugar, BUN, creatinine, calcium, and magnesium with the incidence of cardiac arrhythmias (P < 0.05). However, no significant relationship was noted between Hb and sodium levels with the incidence of cardiac arrhythmias (P < 0.05). Conclusions: The changes in potassium levels increase the risk of cardiac arrhythmias and their complications.