Inferior myocardial infarction results in Q waves in the inferior leads of the electrocardiogram (ECG). Left anterior hemiblock results in initial r waves in these leads. Thus the diagnosis of one in the presence of the other is difficult. It has been reported that inferior infarction can be diagnosed in the presence of left anterior hemiblock when there is a q wave or q equivalent in lead II, and that part of the inferior wall must be spared, to result in the initial r waves of left anterior hemiblock in leads III and aVF. We examined these concepts in 18 patients with such an ECG, by means of resting myocardial perfusion (thallium-201) scintigraphy. In 15 there were defects in the inferior left ventricular wall consistent with inferior infarction. In all of these patients there was sparing of part of the inferior wall: in nine, sparing of the posterior part, and in six, sparing of the anterior part. We conclude that in apparently isolated left anterior hemiblock, a q wave or q equivalent in lead II is an important sign, indicating the likelihood of associated inferior infarction.