It's the top 40 (or 20?) followed people on HC. It's calculated by #following you minus #ignoring you.
If you don't post in I think 2 weeks then you are considered 'inactive' and lost the heart no matter what your following/ignore ratio is.
So if you're the "40th" heart then you will yo-yo in and out of it for a while with whomever else is at a similar follow/ignore ratio to you until you take the lead and put enough distance between yourself and #41.
I just followed you, and no doubt others who weren't following you reading this now might, so, good luck getting it back by your next post
