Histopathological examination of concept of left hemiblock.

This paper is concerned with a histological study of the left bundle-branch system in 20 hearts from patients without conduction defects and in Io heartsfrom patients with left anteriorfascicular block. In addition to the well-known anterior and posterior fasciculi, the left branch was observed to give off a third radiation in II out of the 20 control hearts. This easily identified structure travelled to the midseptal area and emerged either from the common left bundle (5 cases) or from the anterior (3 cases) or posterior radiation (3 cases). In the remaining 9 instances, the septal