idioms

heartsick (very depressed or unhappy) She was really heartsick to learn of your divorce. He was absolutely heartsick over the loss of his ring.

Heartless (uncaring, inconsiderate, merciless) A heartless thief stole his wheelchair. Your father couldn’t be so heartless as to disown you.   envocabulary.com  

heartfelt (strongly felt, sincere) They sent a heartfelt message of thanks to everyone who helped. My heartfelt sympathy goes out to the victims of the war.     envocabulary.com

harden your heart (make yourself stop caring or not feel pity for someone) She tried to harden her heart and tell him to leave. Molly hardened her heart against him.     envocabulary.com

hand on heart (swear that something is true) Are you telling me, hand on heart, that you will never read my private messages? I can put my hand on my heart and say that I’ll never leave you.     envocabulary.com