The hospital course and serial vectorcardiograms of 56 consecutive patients with acute inferior wall myocardial infarction were reviewed. Left anterior hemiblock (LAH) complicating inferior wall myocardial infarction was diagnosed by vectorcardiographic criteria. Seven patients (12.5%) developed LAH between the first and third hospital day, while 49 patients did not. There was no significant difference between these two groups when compared for age, sex, incidence of congestive heart failure, atrial and ventricular arrhythmias, atrioventricular (A V) block, hospital mortality, and previous hypertension, diabetes mellitus, and myocardial infarction. The authors conclude that LAH is a relatively common complication of acute inferior wall myocardial infarction, with no apparent effect on the clinical course.