Final answer:
The primary parasympathetic innervation of the heart comes from the vagus nerve (cranial nerve X).
Explanation:
The primary parasympathetic innervation of the heart is supplied by the vagus nerve (cranial nerve X). The vagus nerve regulates heart rate and other autonomic functions in the heart through its parasympathetic fibers. In contrast, sympathetic nerves also play a role in heart innervation, but the primary focus of this question is on the parasympathetic aspect provided by the vagus nerve.
Learn more about Cranial nerves and heart innervation here:
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