be heartless—be callous, unfeeling, or cruel:
- He made up his mind that I was heartless and selfish.
not have the heart—(also: have no heart)
1. have no inclination or enthusiasm for smth.:
- It was the most miserable meal … and I had not the heart to propose the Loyal Toast at the end.
2. be not cruel or courageous enough to do smth.:
- I should scold you but I am so glad to see you that I have not the heart.