ABSTRACT Objective: Acute myocardial infarction is a leading cause of morbidity and mortality worldwide. Electrolyte imbalance among patients with acute myocardial infarction is not uncommon. The aim of the present study is to assess the status of serum sodium and potassium and plasma atrial natriuretic peptide level among patients with acute myocardial infarction complicated with cardiac arrhythmia. Design: A case control study. Setting: Ibn-Sena hospital/ Mosul-Iraq. Participants: the study included 92 patients with acute myocardial infarction, divided into 2 group; Group I, included 44 patients with uncomplicated acute myocardial infarction; group II, included 48 AMI patients complicated with cardiac arrhythmia. The study also included 50 apparently healthy volunteers as a control group. Methods: Plasma level of atrial natriuretic peptide, serum concentration of sodium, potassium were measured. Results: The results of the study showed a significantly low serum sodium and potassium concentration in patients with AMI (p< 0.0001 and p<0.0001) in comparison with control group. The means of plasma level of atrial natriuretic peptide was significantly higher in patient with acute myocardial infarction in comparison with control group (p< 0.0001), atrial natriuretic peptide level was also higher in patient with complicated acute myocardial infarction in comparison with uncomplicated group (p< 0.0001). A significant negative correlation was observed between plasma atrial natriuretic peptide and serum sodium concentration in patients with uncomplicated acute myocardial infarction (r =-0.825, p<0.0001) and complicated acute myocardial infarction (r =-0.884, p<0.0001). Conclusion: In acute myocardial infarction, electrolytes imbalance is a common fining and usually associated with a variety of cardiac arrhythmia, plasma level of atrial natriuretic peptide significantly increased in patients with acute myocardial infarction and negatively correlated with serum sodium concentration.