cry (one's) heart out

cry (one's) heart out

To cry for an extended period of time. Poor Jane really cried her heart out during the funeral service. I can't watch those sappy movies because I just cry my heart out every time.
See also: cry, heart, out
Farlex Dictionary of Idioms.

cry one's heart out

 and sing one's heart out; play one's heart out; sob one's heart out
Fig. to do something with vigor or intensity. She suffered such grief—alone and sobbing her heart out. The bird sang its little heart out each morning.
See also: cry, heart, out
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs.

cry your heart out

or

sob your heart out

INFORMAL
COMMON If you cry your heart out or sob your heart out, you cry a lot. Note: The heart is traditionally regarded as the centre of the emotions. I threw myself on to the bed and cried my heart out. I had never known her cry, and here she was sobbing her heart out. Compare with your heart out.
See also: cry, heart, out
Collins COBUILD Idioms Dictionary, 3rd ed.
See also:
  • cry heart out
  • cry your heart out
  • cry one's eyes out
  • cry your eyes out
  • cry
  • cry (one's) eyes out
  • cry eyes out
  • cry like a baby
  • cry from the heart
  • a cry from the heart