The normal sequence of electrical activity in the heart is from the sinus node, where the pacemaking impulse originates to the atrioventricular (AV) node, where there is a slight delay in transmission, and thence to the atrioventricular fascicle (fasciculus atrioventricularis, His bundle) for rapid conduction into the branches distributing to the two ventricles. His bundle represents the most vulnerable part of the entire conduction system. A relatively small area of injury may completely block or seriously impair the transmission of impulse. The purpose of the present review is to summarize the information about the His bundle in animals, to compare its morphological features in different animal species and to discuss its embryology and blood supply.

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