To stop being mean; be kind, generous, or sympathetic.
"Сжальтесь", "помилосердствуйте" и т.д.
"Have a heart," I told my supervisor when he said that I must work the whole weekend.
"Сжальтесь", сказал я своему начальнику, когда он сказал, что я должен работать все выходные.
Have a heart, Bob, and lend me two dollars.
Have a heart, Mary, and help me with this lesson.
He didn't know if the teacher would have a heart and pass him.