The most useful criteria for the ECG diagnosis of ischemia/infarction in the presence of left bundle branch block include the development of serial changes in the ST segment and QRS complex in association with clinical manifestations of ischemia, as occurred in the first patient (pages 6.4.1.and 6.4.2); and ST segment elevation in leads with an upright QRS complex, i.e. concordant ST elevation, as was present in the second patient (page 6.4.4).