The heart (♥) has long been used as a symbol to refer to the spiritual, emotional, moral, and in the past, also intellectual core of a human being. As the heart was once widely believed to be the seat of the human soul, the word heart continues to be used poetically to refer to the soul, and stylized depictions of hearts are used as prevalent symbols representing love.

In religious texts the heart was historically ascribed much mystical significance, either as metaphor or as an organ genuinely believed to have spiritual or divine attributes.^{[citation needed]}

In Egyptian mythology, the heart portion of the soul was weighed in a balance against the feather of Ma'at, symbolising truth, in the judgment of the dead in the Egyptian Book of the Dead. Egyptian sources do not actually reveal whether the heart had to be lighter than the feather for the deceased to pass into paradise—all depictions show only the weighing of the heart, not the actual results, heavier or lighter.

Similarly, in the Bible, this idea emerges in the earliest passages; Genesis 6:5 situates the thoughts of evil men in their hearts, and Exodus 5 through 12 speak repeatedly of the Lord "hardening Pharaoh's heart." By this it is meant that God made Pharaoh resolve not to let the Israelite slaves leave Egypt, in order to bring judgment against Pharaoh and demonstrate his power: "'Go to Pharaoh, for I have hardened his heart and the hearts of his officials so that I may perform these miraculous signs of mine among them'" (Exodus 10:1). In the Book of Jeremiah 17:9, it is written that the Lord is the judge who "tries" the human heart.