This '80s-flavored tune finds frontman Gerard Way singing about the romantic ideals of leaving the small town for the bright lights of the big city, and being saved by rock and roll on a Saturday night. "It's a fictional, metaphorical song really, but one about leaving home and running away – about doing whatever you can to run away," he told Tom Bryant, author of Not the Life It Seems: The True Lives of My Chemical Romance. "Because that's the point of starting a band – you get in the van to run away."
My Chemical Romance hit a low after they scrapped the first incarnation of Danger Days and replaced producer Brendan O'Brien with Black Parade helmsman Rob Cavallo. Frontman Gerard Way told Billboard magazine how the band revamped this song after originally recording it for their first version of the record. "'Bullet Proof Heart' is a song we originally recorded for the first version of the record, but we just really loved it and always kept coming back to it. I think it was the last one we tracked - it was kind of a final-hour tracking but we did a heavy amount of work on it to get it to live on Danger Days. When we were making the first version of the record, the song started as an early sign of, 'Hey, maybe you guys you should do something even with a high concept - you should really use your imaginations.' And it was an early sign that I kind of ignored. So that's why I talked about laser beams and running from cops. It has those themes in there, and it was the first song from the first session that had those themes."
1980s heavy metal bands such as British outfit Judas Priest inspired this song. Way explained to Spinner: "That song actually reminded me in an odd way of all the best stuff of '80s what is called cock rock, but not all of it was. Judas Priest is considered metal, but it's great rock 'n' roll. It's having nothing to do with that era of metal, the hair rock, but then having everything to do with like the birth of power-anthem metal."
The song was originally titled "Trans-Am," inspired by Way's newly acquired 1979 Pontiac Trans Arm motor car. He told Q magazine before he changed the title: "It's all about getting in the car, hitting the gas and no one able to stop you. It's large and bombastic. It feels like West Side Story with laser guns."
The song includes the lyric "Jenny could you come back home?" Way told Spin
magazine: "I think my Jenny is referring to the missing Jenny in the Killers song
. I think, somehow, it was inspired by that - there's definitely some connection."