The ECG is an integral part of the diagnostic work-up of patients with suspected MI and should be acquired and interpreted promptly (i.e. target within 10 min) after clinical presentation (2). Dynamic changes in the ECG waveforms during acute myocardial ischemic episodes often require acquisition of multiple ECGs, particularly if the ECG at initial presentation is non-diagnostic. Serial recordings in symptomatic patients with an initial non-diagnostic ECG should be performed at 15–30 min intervals or, if available, continuous computer-assisted 12-lead ECG recording. Recurrence of symptoms after an asymptomatic interval are an indication for a repeat tracing and, in patients with evolving ECG abnormalities, a pre-discharge ECG should be acquired as a baseline for future comparison. Acute or evolving changes in the ST-T waveforms and Q waves, when present, potentially allow the clinician to time the event, to identify the infarct-related artery, to estimate the amount of myocardium at risk as well as prognosis, and to determine therapeutic strategy. More profound ST-segment shift or T wave inversion involving multiple leads/territories is associated with a greater degree of myocardial ischemia and a worse prognosis. Other ECG signs associated with acute myocardial ischemia include cardiac arrhythmias, intraventricular and atrioventricular conduction delays, and loss of pre-cordial R wave amplitude. Coronary artery size and distribution of arterial segments, collateral vessels, location, extent and severity of coronary stenosis, and prior myocardial necrosis can all impact ECG manifestations of myocardial ischemia (36). Therefore the ECG at presentation should always be compared to prior ECG tracings, when available. The ECG by itself is often insufficient to diagnose acute myocardial ischemia or infarction, since ST deviation may be observed in other conditions, such as acute pericarditis, left ventricular hypertrophy (LVH), left bundle branch block (LBBB), Brugada syndrome, stress cardiomyopathy, and early repolarization patterns (37). Prolonged new ST-segment elevation (e.g. >20 min), particularly when associated with reciprocal ST-segment depression, usually reflects acute coronary occlusion and results in myocardial injury with necrosis. As in cardiomyopathy, Q waves may also occur due to myocardial fibrosis in the absence of CAD.