What is it to Speak from the Heart?

I am pleased to have permission to "write from the heart" in this journal.
However, I am dismayed to discover that I don't know how.
I feel I can be clear about the nature of a journal, but feel confusion and dismay about writing from the heart.

"Journal" comes from "journey." A journey originally meant a day's travel. So, in this journal I write of my journey through this day. I might write forever just in describing that which is before my eyes at this moment. Can I use my heart to limit my writing?
To "journey" is to travel from one place to another. In this journal, how can I say where I have begun this day? Can my "heart" identify worthy starting places and stopping places? Can a heart and a mind cooperate?
Well, I can say that in this journal that I may write of daily happenings. Where do those happenings occur? On a stage before me? In my mind? In my heart?
Of what do the happenings of my day consist? What are those happenings made of. Which ones are worth writing about?
Some wise men have suggested that the examined life is more worthy than the unexamined one.
Guess the same goes for a day in that life. It seems that examining is largely a mental activity.
It seems that my worthy happenings consist of my interpretations, assumptions, perceptions, understandings, determinations, accountings. Seems to be head work rather than heart work.

It seems that this journal is to contain writings about the happenings of a day that have a starting place, a stopping place, and the trip connecting them. The trip will consist largely of examanings and meaningings, but where is the heart in that?