A patient with acute extensive anterior and old inferior wall myocardial infarction developed left anterior hemiblock, resulting in loss of the electrocardiographic evidence of infarction. While the vectorcardiogram has generally been found useful in diagnosing coexistent hemiblock and inferior myocardial infarction, serial vectorcardiographic studies failed to identify myocardial infarction masked by the development of left anterior hemiblock in this case. This report highlights the occasional diagnostic problem posed by the association of this conduction abnormality with myocardial infarction and emphasizes the need for careful evaluation of patients with history of chest pain and left anterior hemiblock on the electrocardiogram.