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.
(..) What the... Anna! Help. Anna. Oh no. Olaf? Olaf. Get away from there. So this is heat... I love it. Ooh! But don't touch it! So, where's Hans? What happened to your kiss? I was wrong about him. It wasn't true love. Huh. But we ran all the way here? Please Olaf, you can't stay here, you'll melt. (..)2013 Frozen
(..) Oh, I don't know why but. I've always loved the idea of summer, And Sun, and all things hot. Really? I'm guessing you don't have much experience with heat. Nope! But sometimes I like to close my eyes and imagine what it'd be like when summer does come. Bees'll Buzz, Kids'll blow dandelion fuzz. (..)2013 Frozen