Background; Magnesium has been implicated in the pathogenesis of acute myocardial infarction and its related complication like arrhythmia. Magnesium helps in myocardial metabolism, inhibits calcium accumulation and myocardial cell death. It has role in improving the vascular tone, peripheral vascular resistance, after load and cardiac output, reduces cardiac arrhythmias and improves lipid metabolism. Magnesium reduces vulnerability to oxygen derived free radicals, improves endothelial function and inhibits platelet function including platelet aggregation and adhesion. Objective: To know the relationship between the serum magnesium levels and arrhythmias in patients with acute myocardial infarction.70 cases of acute myocardial infarction, admitted in a tertiary care hospital over a period of 2 years i.e., between October 2015 to October 2017. Results: There is a signicant difference in the magnesium levels in patients with arrhythmias and without arrhythmias. Conclusion: In acute myocardial infarction, patients with low magnesium levels are more prone to get arrhythmias. That is the reason magnesium treatment can be considered in patients of acute myocardial infarction with low magnesium levels.