Innervation of the heart

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The heart has extrinsic and intrinsic innervation, which allows the heart to continue beating if its nerve supply is disrupted (e.g. in cardiac transplant).

The extrinsic supply is from parasympathetic (from the vagus nerve) and sympathetic nerves from both the superficial and deep cardiac plexuses, which provide post-ganglionic fibers to the sinoatrial (SA) and atrioventricular (AV) nodes, as well as other parts of the cardiac conduction system.

The cardiac conduction system represents the intrinsic component and is composed of:

sinoatrial (SA) node
internodal connections
atrioventricular (AV) node
bundle of His
right and left bundle branches
Purkinje fibers

Cardiac myocyte conduction spreads through the heart from myocyte-to-myocyte starting at the SA (pacing) node and then via other parts of the cardiac conduction system in turn as outlined above.

Each part of the cardiac conduction system has its own intrinsic pacemaker, which means that if a higher pacing center (e.g. SA node) is damaged and stops functioning a lower pacing center (e.g AV node) can take over.