Ok, here's where a little English nuance enters the discussion. "Bless your heart" and bless his heart" are often used to say something nice when you really mean something not-so-nice. Here, context is very important because it is also used in the religious sense quite benevolently.
Negative Example: If my sister-in-law leaves a mess for me to clean up, I'll say "bless her heart" instead of "Why can't that dragon clean after herself?".