Reperfusion therapy has become an established treatment for ST-segment elevation acute myocardial infarction (STEMI), increasing the need for early diagnosis and early treatment. Despite the development of diagnostic strategies, the electrocardiogram (ECG) plays a central role in the diagnostic pathway for STEMI because it is inexpensive, readily available, and noninvasive. Moreover, in the acute phase of STEMI, the ECG can provide useful information about the extent of area at risk, the degree of myocardial damage, reperfusion injury, and myocardial reperfusion, all of which influence infarct size. This review explores the clinical importance of the ECG for patients with anterior wall STEMI in the current interventional era. (Circ J 2012; 76: 32-40)