“Warm Blood” is about a passionate crush, and was co-written and co-produced by Rostam Batmanglij, who was formerly the multi-instrumentalist of Vampire Weekend.

Carly deliberately sought producers outside the traditional pop realm in order to expand her sound:

Well, with Rostam, we made what’s maybe one of my favorite songs. It’s really strange… It’s one of my top favorites of all of them. I think the luxury that I had with the two years of taking this break and doing the New York and Broadway thing gave me time to experiment. I wrote with some of the biggest pop writers, and then I wrote with people who I just admired myself with my taste, which is a little bit more left of center.

Jepsen did not set out to make a song called “Warm Blood.” She explained to Complex that “The song’s hook was originally ‘Warm love feels good.’ And I sang it to Rostam, and he was like, ‘Did you say “Warm blood feels good”?’ And I was like, ‘No!’ And he’s like, ‘I love it.’”

Rostam had previously released a “Call Me Maybe”/Annie Lennox mashup in 2012.