Since some people are unable to view the video, I'm posting a transcription done by Realitydistortd from the Heartagram forum & HIMfected St Team. The transcription is as follows:

Heartkiller was originally called “The Biblical Sense,” it was one of the songs we wrote – one of the last ones from the album but it came together from little bits and bobs we’ve being playing around for months and months, which never found their own place and under the banner of Heartkiller they found a home. And it could actually be the first single, so I don’t know.

Yeah, it’s just a direct song about, you know, letting your inner hermit go for a little bit and opening up the door for new possibilities and not being afraid of new things and thing that may hurt you. It just – walk into the scorching sun and just remembering to wear your shades. Reanimation is always a good symbolic value when it comes to being waken up from the dead by romance.

Chorus: “Sparks will fly beneath the luna alight/ Lazarus and frankensteins/ Babe, I’ll be a flatliner for a heartkiller/ Together we die above the lesser light", the lesser light being the moon, so it’s me saying we’re above the moon. It’s me trying to make Elvis Presley’s, "Let Me Be Your Teddy Bear", as complicated as possible, as always. It worked out that I’m always smiling when I’m singing that song, so in that sense, it worked out perfectly. And it’s also, lyrically, it’s kinda – it’s always interesting to myself that I do have the tendency of not having the courage to not being really direct. I was laughing at myself, finding myself in the same spot trying to say very simple things but again making them as complex as possible. The song is full of hope, and so is a lot of the album, and I guess that’s the difference with the last one we did, which was more doomy in its approach – I thought that all hope was lost but then again I accosted in the surprise that there may be a chance for a need to be more happy than in misery