Background: Arrhythmias are common in the first hours after myocardial infarction. Electrolytes imbalance often contribute to the development of cardiac arrhythmias. Aims of the study to show the correlation between serum potassium and calcium and development of post myocardial infarction ventricular fibrillation and to assess the effect of different age groups and gender in the development of this arrhythmia. Patients and method: Ninety three patients, 66(70.96%) males and 27 (29%) females were studied. The mean age was 57.13±11.86 years. Patients included were those who were admitted to the cardiac care units with acute myocardial infarction in 4 hospitals in Basra (southern of Iraq), blood samples for Potassium and Calcium were taken upon admission. Results: Forty (43%) patients had developed primary ventricular fibrillation. The incidence of primary ventricular fibrillation was greater among patients with serum Potassium ≤3.5mmol/L and >4.5mmol/L (p value=0.002). Age was not associated with increased frequency of primary ventricular fibrillation in patients with abnormal serum Potassium, but the incidence of primary ventricular fibrillation as caused by abnormal serum Potassium level was higher among females. No increase in primary ventricular fibrillation was found in patients with abnormal serum Calcium. Conclusions: The incidence of post myocardial ischemic primary ventricular fibrillation was very common in patients with serum Potassium ≤3.5mmo/L and >4.5mmol/L.