Epimyocardial excitation is delayed in areas overlying infarcted myocardium. On the assumption that a delayed R peak in V6 could indicate anterior myocardial infarction (AMI) in the absence of diagnostic Q waves, the findings of angiocardiography (n = 148) and thallium scanning (n = 46) of 194 patients with suspected coronary heart disease (CHD) were compared with regard to two criteria: A (R peak in V6 precedes S peak in V2, or both peaks occur simultaneously, n = 158) and B (R peak in V6 is later than S peak in V2 [R peak delay in V6], n = 36). Of 92 patients with unconfirmed CHD, 4 fit criterion B, and 3 of these had hypertensive heart disease. In 102 patients with confirmed CHD, B was present in 15 of 79 evaluated with angiocardiography and in 17 of 23 patients who had nuclear scanning. Anterior akinesis or dyskinesis was more prevalent in group B (13 cases, 86%) than in group A (17 cases, 26.6%; p = 0.000), as were irreversible anterior thallium defects, with 16 cases in group B (94.1% and 3 cases in group A (50%) (p = 0.016). Two of the three false positives had anterior hypokinesis and one had hypertensive cardiovascular disease. B was less sensitive (59.2%) but demonstrated a specificity of 95.2% and a positive predictive value of 80.6% for the detection of AMI. If used in conjunction with C (poor or reverse R wave progression from V1 to V4, notching at the R upstroke or rsR' in V4, V5, or V6), sensitivity was decreased (38.6%) but false positives were eliminated (specificity and positive predictive value reached 100%). Thus, in the setting of CHD, B can be recommended as a marker of non-Q wave AMI, and its diagnostic reliability is maintained, even in systemic arterial hypertension, if C is taken into consideration.