If you harden your heart, you force yourself not to feel love or sympathy for someone or something. Note: The heart is traditionally regarded as the centre of the emotions. The weeping continued. Lionel hardened his heart against the sound. The government's violent response to the mass action will only harden the people's hearts against the ruling party. Note: You can also say that your heart hardens. Anna saw the hurt in her father's eyes and her heart hardened.