We reviewed electrocardiograms of 23 patients with intermittent left bundle-branch block. A characteristic electrocardiographic pattern consisting of right and mid-precordial deep symmetrical T-wave inversions was detected during normal conduction in 19 of the 23. Of the seven patients who had cardiac catheterization, only two had findings suggestive or organic heart disease and only one had significant obstructive coronary disease. Thus we conclude that patients with intermittent left bundle-branch block frequently have T-wave inversions in right and mid-precordial leads during normal conduction that do not necessarily reflect coronary disease. These T-wave changes are similar to those after termination of chronic right ventricular pacing (left bundle-branch pattern), suggesting that both patterns of abnormal ventricular activation can produce abnormal repolarization when activation returns to normal.