Dopey old me. I thought it expressed admiration. A thousand apologies and I’ll never bless anybody’s heart again.
It probably depends where you are from. I was northern-raised but most of my family is in the Carolinas. It took me a while to catch on to honey-dipped barbs, so “bless your heart” and especially “bless her heart” behind someone’s back raises suspicions. But if you come from a place where there’s no sting in it, carry on, because blessings are and ought to be a good thing.