From Longman Dictionary of Contemporary Englishbust a gutbust a gut (also bust your butt/ass American English spoken) informalTRY TO DO OR GET something to try extremely hard to do somethingI bust a gut trying to finish that work on time. →bust
Examples from the Corpus
bust a gut• The movie was hilarious. I just about busted a gut.• We busted a gut trying to get home on time.