It's a very endearing and affectionate way to refer to someone you love, like a child, a partner, or even a pet. It conveys a sense of tenderness and fondness.
Here's a breakdown of the words:
* Mi: My
* Corazón: Heart
* -ito: A diminutive suffix that adds a sense of smallness and endearment
So, "mi corazonsito" is like saying "my little sweetheart," "my darling," or "my precious one."