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.
If someone has a cast iron stomach, they have a strong stomach that can digest unusual food and even bad food without being ill.
Jimmy must have a cast-iron stomach, when he drank milk with lime juice and felt perfectly fine afterward.