Question

If the heart refers to a person's conscience or inner self, is that using synecdoche or symbolism?

Answer 1

Symbolism.

Explanation:

What is known is that the heart refers to the soul, inner self or person's conscience...

These being (theoretically and philosophically), parts of ourselves.

Synecdoche can be understood as a part of a whole relation or viceversa.

Thus, a symbolic reference is much more accurate because it is relatively less general and more specific. It shows a direct relation between the 'objects' acting as 'synonyms'.