Sing (one's) heart out phrase
Sing can also be replaced with work, play, etc to express that you do something with great enthusiasm.
Sing in an extremely enthusiastic way.
All spectators rose to their feet and gave a big round of applause to the girl who had been singing her heart out.
When I have a chance to sing on a big stage, I will sing my heart out.
The verb" sing" must be conjugated according to its tense.
The origin of this phrase is not clear.
A problem or difficult circumstance
I'm short-sighted, so forgetting my glasses is a real hair in the butter for my sight.