After the band finished touring behind their 2008 album When The World Comes Down, All-American Rejects frontman and lyricist Tyson Ritter moved to Los Angeles, where he got into some bad company and lost his way with a toxic girl. During a writing trip in Maine for Kids In The Street with songwriting partner, guitarist Nick Wheeler, the singer found himself struggling to come up with good lyrical ideas. Eventually, he broke through the writer's block by writing the hook for this song after deciding to be candid about the dark place he found himself in. In our interview with Nick Wheeler, he explained, "We had to push each other to think outside of the box and leave our comfort zone. Because we know how to write a catchy song. We could write a B-rate version of 'Gives You Hell' and 'Move Along,' and just borrow the tricks that we used in those songs. But we've never been about that. We've never tried to capitalize on songs and just try to ride the wave. It doesn't last when you do that. For 'Heartbeat's Slowing Down' we definitely pushed each other to really make this something special. And I do think it's the best song on the record."
Ritter told Artist Direct: "There's a lot of regret on the record. Everybody asks me if "Heartbeat Slowing Down" is about somebody dying, I'm like, "No, it's about something I killed." Nick Wheeler told us, "I think that's kind of just uprooting some feelings and it's kind of an apology to somebody in the past."
English singer Mika adds choirboy vocals to this track. Wheeler told Pop Crush about their collaboration: "We tried to emulate a British Boys Choir at the end of it. A lot of the demos we did in the bathroom and in the cabin in Maine ended up on the record of us just 'singing like thisssss' (Wheeler sings in a veryyyyy high pitched voice). In addition to that, we did the record with producer Greg Wells, who has done all of the Mika records. Mika actually was a British choir boy, so he actually came and sang a lot of the tracks on that song, and that was a lot of fun."