Used to describe something you have memorized

It's a misnomer of course, but one that's used all the time

The most trustworthy form of communication is heart to heart between two people.

used when described a deep and intimate conversation between two individuals more often the opposite sex

if you know something in your heart of hearts, you are certain of it although you might not want to admit it.

Knowing something for certain, but not wanting to admit it.

When you really fancy someone and whenever you're around them your heart starts beating faster. Blood flow to the heart, resulting in a heart-on (punned with the more familiar "hard-on"). Sweet!

Courge or bravery