It's Called Heart

When it empty, I will it enable for everyone knock and do something..
When someone knock the door, I will open it..
If I open it, you must quickly enter the door so that I will close the door because you are here..

If you just knock it, but doesn't appear in front of me..
I open the door and will enable the other to come in so that let you regret it..

If I open the door, it means your chance is coming..
But, I won't have waiting you in a long time..
So, please come in soon..

Because it will entered by another if you don't..
Finnaly, you just do regret it..

The things I say is something I called HEART..