"I'm taking on a different look this time around," Lovato told MTV News in February. "I feel like I have my own thing going, like rocker-chic sophisticated, just a different kind of fashion style this time around."

"Heart Attack" recently debuted at No. 1 on the iTunes chart in 18 countries (including the U.S.) and No. 12 on the Billboard Hot 100 chart (the second-best Billboard debut of the year).