Design: single center case-series Prospective study. Setting: Coronary care and cardiac catheterization units of Sohag University Hospital. Study Population: the first 100 Patients (from January 2015 to June 2015) presented with ACS associated with serious cardiac arrhythmias then subjected to elective percutaneous coronary angiography. Results and Conclusion: arrhythmias are the most serious complication of acute coronary syndrome, 74% of patients above the age of (45 years in men and 55 years in women). Serious arrhythmias in patients with ACS are more common in males. The most common arrhythmias in patients with acute coronary syndrome is RAF 29%, the least common type is heart block 11%, the most serious type is VT (18%) which is more common patients presented by cardiogenic shock. According to the coronary angiographic evaluation ACS patients presented with serious arrhythmias are more prone to have 3 vessels disease and LAD is critically diseased in most of those patients (72%).