Demi Lovato delivers! The 'X Factor' judge performed on another singing reality show, this time 'Britain's Got Talent.'

Lovato sang her heart out on 'Heart Attack.' Clad in head to toe black with striking red lipstick, Lovato belted her heart out in front of a lit up set of concentric hearts. Lovatics will eat this up -- and if she were competing, we bet the judges would too.