This electrocardiogram shows an acute extensive anterolateral wall myocardial infarction in evolution. The characteristic features demonstrated here include ST segment elevations in the anterior precordial leads V1 through V6 and in limb lead I. Q waves are present in V1 to V3. The ST segments will, in most cases, return to the baseline as the infarction evolves, while the Q waves remain as the markers of dead tissue. In cases of left ventricular aneurysm, the ST segment elevations may remain.