Total body surface maps from 15 subjects with left bundle branch block and normal axis (LBBB-NA) and 10 subjects with left bundle branch block and left axis (LBBB-LA) were analyzed and compared with maps from normal subjects. In 19 of the 25 subjects with LBBB, the timing of early upper sternal positivity was similar to that of normal subjects, indicative of timely but oppositely directed septal activation. The right ventricular breakthrough was normally located in all, but was earlier after the onset of QRS than expected in some. The initial portion of the positivity produced by left ventricular activation was located in the upper anterior chest in both LBBB-NA and LBBB-LA, but its onset was generally delayed compared with that in normal subjects, presumably because of the time taken by the right-to-left septal activation. Also, the total duration of this positivity was longer than in normal subjects and extended considerably beyond 90 msec, indicating prolonged activation of the anterior free wall of the left ventricle. In LBBB-NA, this upper anterior positivity remained anterior throughout depolarization, but in LBBB-LA it moved toward the left shoulder and the left upper back, presumably due to the posterior orientation of the terminal portion of depolarization. This terminal orientation in patients with LBBB-LA was thought to be due to the additional delay in the activation of the anterobasal portion of the left ventricle caused by selective involvement of the left anterior fascicle.