6.5.3. Parasympathetic Nerve Fibres: Cardiac Branches
These branches leave the main vagus nerve in the neck and they travel downwards to the two cardiac plexuses: the superficial cardiac plexus lies on the inferolateral aspect of the aortic arch. The deep cardiac plexus lies on the anterior aspect of the bifurcation of the trachea (i.e. where the trachea divides to become two bronchi - it is considered 'deep' because the trachea lies posterior to the aortic arch!). These branches contain preganglionic fibres, which will synapse in the cardiac plexus, and continue as postganglionic fibres, which will act to slow the heart rate and force of contraction if stimulated. This applies to the left and right vagus nerves.