Electrocardiogram(ECG) is the first investigation done in case of acute myocardial infarction. ECG in this setting can not only help to diagnose the cause of chest pain to be acute myocardial infarction but also at times it can help to localize the infarct related artery. The presence of ST elevation in particular lead has diagnostic and as well as therapeutic implications. The ECG at presentation can also help to focus on the particular vessel during coronary angiogram and hence coronary angioplasty. This book focuses on the ECG during acute myocardial infarction and how it helps to localize the infarct related artery.