Background: The major drawback of current troponin assays is sensitivity deficit at presentation due to delayed release of circulating levels. Therefore, acute myocardial infarction (AMI) exclusion requires prolonged period of monitoring for 6 to 9 hours and serial blood sampling, the grey zone for troponin elevation, which consequently leads to overcrowding in the emergency department and increases the associated cost every year. As a result, novel biomarkers are continuously in development. A particularly interesting observation is the response of circulating copeptin levels as a result of an acute myocardial infarction. Objective: Comparing the value of serum copeptin assays to serum troponin I for early diagnosis of acute coronary syndrome. Patients and methods:  A prospective non- randomized study will be conducted over 45 patients in National heart institute (NHI). All of the patients were above 40 years old, presented to the emergency department  (ED) within 12 hours of symptom onset of acute chest pain suggestive of acute coronary syndrome. After informed consent and permission from the local administrative authority, all patients were subjected to a thorough history taking, examination, 12- lead ECG monitoring, coronary angiography and echocardiographic assessment. In addition to the routine laboratory investigations. Cardiac troponin I and copeptin were assayed from venous blood samples obtained at admission, then 6 hours later. Based on clinical picture, ECG findings, serial troponin I assays, coronary angiography and echocardiographic findings all of the patients were divided into 3 groups:  1. ST-segment elevation of myocardial infarction (STEMI). 2. Non ST- segment elevation of  myocardial infarction (NSTEMI) . 3. Unstable angina (UA). Results: The admission values of copeptin was significantly different.  At a cutoff value of 30.5 pmol/l, AMI can be diagnosed with 100 sensitivity, 100 specificity, 100 PPV, 100 NPV and accuracy 100%. The admission values for troponin I was significantly different. At cutoff value of 0.23 ng/ ml AMI can be diagnosed with 93.33 sensitivity, 100 specificity, 100 PPV, 88.2 NPV and accuracy 98%. The 6 hours-later copeptin values were also significantly different.  AMI was diagnosed at cutoff value of 32.2 pmol/l with 100 sensitivity, 100 specificity, 100 PPV, 100 NPV and 100% accuracy. The 6 hours later values of troponin I  were significantly different. At cutoff value of 0.23 ng/ml, AMI was diagnosed with 93.33 sensitivity, 100 specificity, 100 PPV, 88.2 NPV and accuracy 98%. Conclusion: The current study provided evidence that measurement of serum copeptin was better than troponin I for early diagnosis of acute myocardial infarction, but could not evaluate the value of copeptin in UA diagnosis versus non -ischemic causes of chest pain.