“Only Heart” is featured on John Mayer’s second studio album, Heavier Things, released in 2003. “There’s a certain swing-for-the-fences feel and a hurried nature that I think you have when you’re making your first record and have much to prove,” Mayer said in an interview with Billboard when the album came out. “Now that I’m in a higher gear, I don’t have to press so hard on the gas, and I’m loving it.”
The track alternates throughout between G minor on the verses and B minor for the chorus.