“I love you with so much of my heart that none is left to protest.”

San Martino del Carso (27 August 1916). [A Major Selection of the Poetry of Giuseppe Ungaretti, 1997, ISBN 9781550960341]
Original: (it) Di queste case
non è rimasto
che qualche
brandello di muro
Di tanti
che mi corrispondevano
non è rimasto
neppure tanto
Ma nel cuore
nessuna croce manca
È il mio cuore
il paese più straziato.

From the poem I Hear an Army http://www.bartleby.com/103/128.html

this is a line spoken by Frank Morgan's depiction of the Wizard of Oz in the 1939 film, which debuted 20 years after Baum's death. It did not actually appear in the "Wonderful Wizard of Oz". The ending of "Steam Engines of Oz" wrongly attributes this phrase to Baum when it would've originated from the 1939 adaptation script writers Langley/Ryerson/Woolf.
Misattributed
Variant: A heart is not judged by how much you love; but by how much you are loved by others
Source: The Wonderful Wizard of Oz

Quotes from Confessions (Spoken word)

" To Anthea, st. 1 http://www.bartleby.com/106/96.html".
Hesperides (1648)

As quoted in "Michael Jackson: Elizabeth Taylor Honors her good friend" http://news-briefs.ew.com/2009/06/elizabeth-taylor-honors-good-friend-michael-jackson.html by Dave Karger, Entertainment Weekly (26 June 2009)]

A Woman's Touch, written with Wayne Perry.
Song lyrics, Blue Moon (1996)

25 Things Even My Best Friends Didn’t Know Until Now (1 October 2009).
Context: In a day, sometimes I feel so much love for the world, I think my heart is bursting. Sometimes, I feel so scared, I want to shrink myself even further. I think that’s what happened to us gods and goddesses. Like the dinosaurs, we realized that it’s too dangerous to be so large. So we kept shrinking ourselves to what we are now. We might get even smaller. I see the sign in the engineers making smaller gadgets, smaller and smaller. Pretty soon, our fingers will be too large to operate them. So what are we doing? I trust in the human wisdom. We are incredibly intelligent beings. So we might know something without thinking that we know…. Well, even my best friend didn’t know until now that I was thinking of crazy things like this.