The sympathetic cardiac nerves are six postganglionic branches of the sympathetic nervous system which run from the cervical ganglia of the sympathetic trunk to the cardiac plexus. They are named after the ganglion from which they emerge:
- superior cervical ganglion: superior cardiac nerve
- middle cervical ganglion: middle cardiac nerve
- inferior or stellate cervical ganglion: inferior cardiac nerve
The nerves descend to the root of the neck with the following relations:
- posterior: prevertebral fascia overlying anterolateral surface of vertebral bodies
- and superior: common carotid artery
- and inferior: subclavian artery
- laterally: sympathetic trunk
Entering the superior mediastinum, they ramify to contribute to the plexuses on the surfaces of the oesophagus and the trachea. However, their major target is the deep part of the cardiac plexus. The exception to this rule is the left superior cardiac nerve which passes over the arch of the aorta anterior to the vagus nerve; it alone contributes to the superficial cardiac plexus.
Sympathetic fibres from the first five thoracic segments also supply the cardiac plexuses.