Bachmann's bundle

Bachmann's bundle is one of the four conduction tracts that make up the atrial conduction system of the heart which is responsible for transmitting the pacemaking impulses of the sinoatrial node to the rest of the heart. Bachmann's bundle originates in the sinoatrial node and is the only tract that innervates the left atrium.

Bachmann's bundle and the atrial conduction system
Besides from Bachmann's bundle, the other three conduction tracts are known as the anterior, middle, and posterior tracts, which run from the Sinoatrial Node to the atrioventricular node, converging in the region near the coronary sinus. Atrial automaticity foci are within the atrial conduction system. The concentration of converging conduction tracts near the coronary sinus results in considerable automaticity activity originating in that area.