It's a phrase used to express sincerity, genuine feelings, and deep emotion.
Here are some examples of how it's used:
* "Te agradezco de todo corazón." (I thank you from the bottom of my heart.)
* "Te quiero de todo corazón." (I love you wholeheartedly.)
* "Lo hago de todo corazón." (I do it wholeheartedly.)
It's a very common and powerful expression in Spanish, often used in formal and informal situations.