Define Heart

If you look up in Webster's Dictionary,
The definition of the word "Heart,"
There are so many ways to define it,
That I do not know where to start.

A hollow muscular organ,
Of animals vertebrate,
That contracts and forces blood,
To flow and circulate.

A playing card marked
With a stylized heart of red,
The compact part of a leafy
Rosette lettuce head.

A game in which the object
Is to avoid taking tricks,
A generous disposition,
I do not know which one to pick.

The central or innermost part,
One’s innermost character,
The most vital part of something,
Perhaps I should defer.

All I know is that mine aches,
Since I let her go.
I feel my body has gone limp,
My blood no longer flows.

The playing card of red
Now looks black as night.
The leafy lettuce has now wilted,
Oh what a terrible sight.

Perhaps I should ask Mr. Webster
To change what he's defined,
For without her my vital, innermost part
No longer wants to shine.