In some work1 recently reported, lesions of the left branch of the auriculoventricular bundle were produced by incising the endocardium of the left ventricle. It was noted that dogs often gave a normal electrocardiogram even after extensive incisions had been made in the endocardium. Later, however, as the heart became dilated because of experimental ligation of coronary arteries, the electrocardiograms were abnormal.
In this paper are recorded further observations that have been made following the division of the right and left branches and the subdivisions of the left branch of the auriculoventricular bundle. The extent to which the subdivisions of the left branch can be divided and the electrocardiogram still remain normal are in a measure determined. It is further shown that some of the atypical electrocardiograms may be brought back to normal.
In a series of thirty dogs2 the right branch was divided in eight instances, the left in