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.
(..) box underneath the window. It sounds like this... It's, uh, it's... it's not evil, buddy, It's, uh, it's a radiator, And the heat makes noise when it comes on. No, it doesn't. It... It's very evil. It's scary to look at. It's... okay... (..)2003 Elf