What's meant by the sentence below?
What's meant by "Grinch's heart grows three sizes and breaks that measuring device"

But there's this other guy. Actually it's the same guy that wells up every time that Grinch's heart grows three sizes and breaks that measuring device... And he's saying, y'know, 'This is too hard! Get out! Get out!'

American slang would drive me to the grave soon or later~!

Question

What's meant by the sentence below?
What's meant by "Grinch's heart grows three sizes and breaks that measuring device"

But there's this other guy. Actually it's the same guy that wells up every time that Grinch's heart grows three sizes and breaks that measuring device... And he's saying, y'know, 'This is too hard! Get out! Get out!'

American slang would drive me to the grave soon or later~!

Answer

If you have a big heart, then it means that you are a very caring person.  The grinch's heart was so big that it broke the scales that it was being measured on.  So the quote is basically saying that the grinch was extremely caring - more caring that anyone else.