Demi Lovato doesn't wear her heart just on her sleeve, but also in her music. Following the chart-topping success of 2012's "Give Your Heart A Break" and this year's "Heart Attack," Demi is once again singing about love on her "The Mortal Instruments: City of Bones" track, "Heart By Heart."

The singer gave fans an early taste of the sultry ballad on Wednesday (July 3) with a minute-long preview posted online.

"When your soul finds the soul it was waiting for/ When someone walks into your heart through an open door/ When your hand finds the hand it was meant to hold/ Don't let go," Lovato sings on the simmering slow jam. As the crescendo builds, she adds, "Someone comes into your world/ Suddenly your world has changed forever."

Lovato joins a diverse batch of artists on the release, including Zedd, Owl City, Jessie J, AFI, Youngblood Hawke and Colbie Caillat, among others. The soundtrack will officially hit retailers on August 20, one day before the movie, starring Lily Collins, is released to theaters. (It also happens to be Lovato's 21st birthday.)

The film, based on the best-selling novel by Cassandra Clare, is about a Brooklyn teen Clary Fray (played by Lily Collins) who learns that she is a member of a race of demon destroyers known as Shadowhunters. The film also stars Jamie Campbell Bower, Jonathan Rhys Meyers, Lena Headey, Kevin Zegers and Godfrey Gao.

Check out everything we've got on "The Mortal Instruments: City of Bones."