A normal ECG should not be a huge source of relief when evaluating patients with possible or confirmed myocardial infarction. 8% of acute myocardial infarctions have a completely normal ECG at the time of presentation, and these patients have a 5.7% in-hospital mortality. Serial electrocardiography can certainly improve the yield of electrocardiography but does not rule out AMI with 100% accuracy.
Like most tests in medicine, the ECG is very useful at ruling in disease, but it is limited at ruling out disease.
[The Prognostic Value of a Normal or Non-specific Initial ECG in AMI. JAMA 2001.]
