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