The ECGs of 72 patients with an unequivocal vectorcardiographic diagnosis of either left anterior hemiblock (LAH) or inferior myocardial infarction (IMI) or both were reviewed. Our intention was to identify definite electrocardiographic criteria for the diagnosis of the left anterior hemiblock and of inferior myocardial infarction when both were present vectorcardiographically. All patients with left anterior hemiblock, accompanied or not by IMI, had a left axis deviation, a negative terminal deflection (S wave) in leads II, III and a VF; the majority of them also had a terminal r wave in lead a VR (50 of 52, 96%). The diagnosis of LAH was therefore always possible in the concomitant presence of both entities. A negative initial deflection (Q wave) significant in size or not significant was present in a minority of patients with both LAH and IMI (9 of 24, 37.5% in lead II; 7 of 24, 25% in lead III; and 12 of 24, 50% in lead aVF). In the patients with insignificant Q waves, as well as in the rest of the patients with rS configuration, the electrocardiographic diagnosis of IMI was not possible due to the concomitant presence of LAH.