The innervation of the heart is provided by the sympathetic part and parasympathetic part of the autonomic nervous system:

The parasympathetic fibers come from the right vagus nerve (CN X) and left vagus nerve (CN X). They reach the heart via the cardiac nerves.
The sympathetic fibers come from both sympathetic trunks (Read more!). They arise within the upper thoracic segments (T1 - T4 / T5) of the spinal cord and reach the heart via the cardiac sympathetic nerves. The preganglionic fibers synapse in the superior cervical ganglion, middle cervical ganglion and inferior cervical ganglion and upper four to five thoracic ganglia of the sympathetic trunks.

Nerve fibers from the sympathetic nervous system and parasympathetic nervous system form a nerve network known as the cardiac plexus. Moreover, the cardiac plexus can be subdivided into two smaller parts, and each person actually has two cardiac plexuses - superficial and deep cardiac plexuses.

The superficial (ventral) cardiac plexus is positioned below the aortic arch between it, the pulmonary trunk and the left pulmonary artery. It lies anterior to the left pulmonary artery. The superficial cardiac plexus contains the superior cervical cardiac branches of the left vagus nerve and inferior cervical cardiac branches of the left vagus nerve.
In contrast, the deep (dorsal) cardiac plexus is found posterior to the aortic arch, lying between it and the tracheal bifurcation. It is composed of the cardiac branches coming from the left and right superior, middle and inferior cervical sympathetic ganglia (except the left superior cervical sympathetic ganglion), cardiac branches of the left and right first four to five thoracic sympathetic ganglia, superior cervical cardiac branch of the left vagus nerve, superior and inferior cervical cardiac branches of the right vagus nerve and cardiac branches of the left and right recurrent laryngeal nerves.

Overall, the parasympathetic system lowers heart rate, reduces the force of myocardial contractions and provides narrowing (vasoconstriction) of the coronary arteries. In contrast, the sympathetic system raises heart rate, increases myocardial contraction force and provides widening (vasodilation) of the coronary arteries.

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Innervation of heart