Under Lock and Key

Last night you gave me your heart, and I took it with joy!
Then you gave me a warning,
because your heart is not a toy.

You asked me for my heart,
I said you can have my heart that's fine.
But not the key,
that's still mine.

Someday I'll give it to you,
Someday it will be yours.
But for now the key is well guarded,
and behind closed doors.

Just so you know,
since I know you can't see.
This heart of mine,
is under lock and key.