It is a broad band of cardiac muscle that passes from the right atrium, between the superior vena cava and the ascending aorta.

[2] Bachmann's bundle is, during normal sinus rhythm, the preferential path for electrical activation of the left atrium.

He found that clamping the muscular bundle of fibers that connects the atria caused a significant conduction delay.

The concentration of converging conduction tracts near the coronary sinus results in considerable automaticity activity originating in that area.

[5] Because it originates close to the sinoatrial node and consists of long parallel fibers, Bachmann's bundle is, during sinus rhythm, the first of these connections to activate the left atrium.