The phrase "heart of hearts" refers to a person's truest and most genuine feelings or beliefs. Synonyms for this phrase can include "core of being," "innermost self," "soul," "essence," and "spiritual center." These words all convey a sense of depth and sincerity in a person's emotional or spiritual makeup, and suggest a profound connection to one's truest nature. When someone speaks from their heart of hearts, they are expressing a deeply personal and authentic truth that goes beyond surface-level emotions or beliefs. Understanding the nuance of these synonyms can help us to appreciate the complexity and depth of human emotion and spirituality.