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.
(..) Words without thoughts never to heaven go Look you lay home to him Tell him his pranks have been too broad to bear And that your grace hath screened and stood between much heat and him Not for all the riches under heaven, I pray you do not push me - Mother! - I hear him coming (..)2015 Hamlet
(..) my lord, with all the vows of heaven I do know when the blood bums how prodigally the soul lends the tongue vows These blazes, daughter, giving more light than heat, you must not take for fire For this time be somewhat scanter of your maiden presence Set your entreatments at a higher rate (..)2015 Hamlet