bundle of His

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The bundle of cardiac muscle fibers that conducts the electrical impulses that regulate the heartbeat, from the atrioventricular node in the right atrium to the septum between the ventricles and then to the left and right ventricles.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun Specialized heart muscle cells that transmit electrical impulses from the AV node in the heart to the muscle cells of the heart wall, which contract in response producing the heart beat.