She's at her best when 'the heat is on'. [=when she feels a lot of pressure; when she needs to finish something quickly]
She said things in 'the heat of the moment' [=when she was angry for a short period of time] that she later regretted.
The company has 'turned up the heat on' [=has put extra pressure on] its employees to finish the job quickly.
(..) Jack gives up the bearings. That night, there was a mutiny. They marooned Jack on an island and left him to die, but not before he'd gone mad with the heat. So that's the reason for all the... Reason's got nothing to do with it. Now, Will, (..)2003 Pirates of the Caribbean: The Curse of the Black Pearl