harden one's heart
Feel no sympathy for, as in We can't afford to give them more; we'll just have to harden our hearts when they ask. [Late 1300s]
Words nearby harden one's heart
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.