User blog comment:Neowitch/700 - Breakfast at Mugiwara's/@comment-4493594-20130227131553/@comment-4754162-20130228034742

I thought Law's pirates were called "Heart" because of his ability to be able to dissect and take out people hearts. Ya know, since he give 100 hearts to WG for the Shichibukai post and during PH he took out the hearts of his, Monet and Smoker, stuff like that.

When Vergo said about reserving the Heart seat foreshadows what we see today, but since Law never took the seat, I doubt the name of his crew originated or was defined from Doflamingo's theme.