You can know something with your head, but to know something in your heart is not to go on emotions, but is to instill knowledge into your very being. Whatever you decide to put in your "heart" will ultimately control how you think and act.
That is why it is important to be aware of the things you see and hear, the places you go, and the things that you say.
Matt. 15: 18 "But those things which proceed out of the mouth come forth from the heart; and they defile the man."
Both actually, but I listen to my heart and then decide if what my heart wants is reasonable. My heart has never let me down, but over thinking things has.
That is why it is important to be aware of the things you see and hear, the places you go, and the things that you say.
Matt. 15: 18 "But those things which proceed out of the mouth come forth from the heart; and they defile the man."
"When it comes to making important decisions, I can't trust my heart; that bitch is straight retarded."
*lolz