harden your heart against somebody/something

harden (one's) heart against (someone or something)

To stop or keep someone from feeling kindness and compassion towards someone or something. I worry that all the trauma she's already been through at such a young age will harden her heart against other people.
See also: harden, heart

ˌharden your ˈheart against somebody/something

no longer be emotionally affected by somebody/something because you feel angry, bitter, etc., towards them/it: Doctors have to harden their hearts against the suffering they see every day.