BACKGROUND: One of the causes of mortality in acute myocardial infarction (AMI) is ventricular tachycardia. Abnormal serum Potassium (K) level is one of the probable causes of ventricular tachycardia in patients with AMI. This study carried out to determine the relationship between serum potassium level and frequency of ventricular tachycardia in early stages of AMI. METHODS: Ina cross-sectional study on 162 patients with AMI in the coronary care unit (CCU) of Nour Hospital (Isfahan, Iran), the patients' serum potassium level was classified into three groups: 1) K<3.8 mEq/l, 2) 3.8≤K<4.5 mEq/l and 3) K≥4.5 mEq/l. The incidence of ventricular tachycardia in the first 24 hours after AMI was determined in each group by chi-square statistical method. RESULTS: The frequency of ventricular tachycardia in the first 24 hours after AMI in K< 3.8 mEq/l, 3.8≤K<4.5 mEq/l and K≥4.5 mEq/l groups were 19.0%, 9.6% and 9.9% respectively. The high frequency of this arrhythmia in the first group as compared with the second and the third group was statistically significant. CONCLUSION: Hypokalemia increased the probability of ventricular tachycardia in patients with AMI. Thus, the follow up and treatment of hypokalemia in these patients is of special importance. Keywords: Acute Myocardial Infarction, Ventricular Tachycardia, Hypokalemia, SerumPotassium Level.