have (one's) (best) interests at heart
To be primarily concerned with what would benefit one. I know you don't agree with some of the decisions I've made, but you have to trust that, as your mother, I have your best interests at heart.
have someone's best interest(s) at heart
to make decisions based on someone's best interests. I know she was only doing what would benefit her, but she said she had my best interests at heart.