Bundle branches are clusters of pathways that carry electrical impulses to different parts of your heart. A bundle branch block is a delay or obstruction in one of the pathways. These can keep your heart from pumping normally. Many blocks are caused by heart disease, some are there at birth. If the condition is serious, a pacemaker may be prescribed. The key bundle is the bundle of His, the "him" in question being the discoverer, Wilhelm His, Jr. This bundle distributes the electrical impulse from the AV node to each ventricle, where it branches into the left and right bundle branches.