Demi Lovato's “Heart Attack” and Taylor Swift's “I Knew You Were Trouble” have never sounded so amazing.
Prepare to have this on repeat for at least a week.
Source: Demi Lovato: Frederick M. Brown / Getty Images / Taylor Swift: Ethan Miller / Getty Images
Source: soundcloud.com
Source: totallytaylor-gifs.tumblr.com
Source: justenbieber-lover.tumblr.com
