@Delia , in the South, “bless your heart” is more like a tool than a fixed meaning. Tone, timing, and context do most of the work.
It can absolutely be sincere. Someone brings you food when you’re sick, helps you fix something, or hears you went through a rough time, and they’ll say it with genuine warmth. In that case it really does mean kindness or sympathy.
It can also soften bad news or criticism. For example, if someone says something obviously wrong or naive, a “well, bless your heart” might be a polite way of saying “you don’t know what you’re talking about” without being blunt.
And yes, sometimes it’s used as a quiet insult. Usually you can hear it in the tone or see it paired with a look or a follow-up comment that makes the meaning clear.
Oh and then there's how I used it in my earlier post. It was just a nod of empathy.
Like a lot of Southern expressions, it’s less about the words themselves and more about how they’re delivered.