The bundle branches are the main conduits that carry the heart's electrical impulses to the Purkinje fibers.
Normal depolarization begins at the AV node and travels to the beginning of the left bundle branch.
The left bundle branch splits into the anterior fascicles which feeds the anterior left ventricle, and the posterior fascicles which feed the posterior left ventricle. The right bundle branch feeds the right ventricle. A bundle branch block indicates a conduction problem which may be produced by a myocardial infarction or other underlying heart disease. Bundle branch blocks can occur in the left or right bundle branch or in both. A 12-lead ECG will usually indicate which side is affected.