Demi Lovato & Jason Derulo Heat Up The iHeart Radio Music Festival In Vegas

Demi Lovato shows off her curves backstage at the 2015 iHeartRadio Music Festival held at MGM Grand Garden Arena on Friday night (September 18) in Las Vegas.

The 23-year-old “Cool For the Summer” singer kept it hot in the arena where she performed alongside Sam Smith, Disclosure and Jason Derulo — who just hated his shirt so much, he had to take it off.

PHOTOS: Check out the latest pics of Demi Lovato

“Morning VEGAS. Don’t worry I am excited to be here – that’s just my ‘Jetlag is a b****’ face,” Sam wrote on Instagram just hours before hitting the stage.

25+ pics inside of Demi Lovato, Sam Smith and Jason Derulo…