MICHEL MARTIN, HOST:
Let's talk about the Grinch. He's best known for his psychological problems.
(SOUNDBITE OF SONG, "YOU'RE A MEAN ONE, MR. GRINCH")
THURL RAVENSCROFT: (Singing) You're a foul one, Mr. Grinch. You're a nasty-wasty (ph) skunk.
MARTIN: Definitely some anger and empathy issues there, and he did try to steal Christmas. But NPR science correspondent Jon Hamilton wanted to understand the Grinch's physical challenge, a heart that was two sizes too small.
JON HAMILTON, BYLINE: So I went to see a guy who specializes in hearts. His name is David Kass. He's a cardiologist at Johns Hopkins University, and he's been thinking about the Grinch.
DAVID KASS: Tough problem, tough problem 'cause heart at least reputedly is two sizes too small. We in fact don't see this very much.
HAMILTON: Kass says there are conditions that effectively reduce the size of the heart, and they're no fun.
KASS: You're just going to have to have that small heart beating twice as fast. So that means you're going to feel your heart racing all the time.
HAMILTON: Which could make you grumpy. And it would definitely make it hard to do physical labor. So how did the Grinch shimmy up all those chimneys and carry off every Christmas present in Whoville? I ask Kass if that would have even been possible for someone whose cardiac output was so limited.
KASS: No. He would be doing more traditional grinchy things - just sitting around, moping.
HAMILTON: Anyway, from a cardiologist point of view, the story takes an even more remarkable twist.
(SOUNDBITE OF FILM, "HOW THE GRINCH STOLE CHRISTMAS!")
BORIS KARLOFF: (As Narrator) And what happened then? Well, in Whoville they say that the Grinch's small heart grew three sizes that day.
HAMILTON: Kass says this is possible, sort of.
KASS: There are situations where the human heart can fairly rapidly get large.
HAMILTON: Like when a valve suddenly ruptures.
KASS: But you don't feel good when that happens. This couldn't be Grinch's issue.
HAMILTON: So Kass has a different explanation.
KASS: He's really a snake. I mean, not just any snake - he's a python.
HAMILTON: Specifically a Burmese python. That makes sense because the heart of a Burmese python is designed to grow rapidly after a big meal, like, say, a roast beast.
KASS: That would do it. His heart would get large, yeah.
HAMILTON: But Kass says the big meal hypothesis isn't perfect.
KASS: When a snake like a python has done that, does he, like, run around lifting sleds and doing - no. He looks like all of us after Thanksgiving. You know, we're on the couch. If we can watch TV, yeah, that's about it.
HAMILTON: So even a big-hearted Grinch probably would not have returned those toys to every family in Whoville. Jon Hamilton, NPR News.
(SOUNDBITE OF SONG, "WELCOME CHRISTMAS")
UNIDENTIFIED SINGERS: (Singing) Welcome Christmas while we stand heart to heart and hand in hand. Fahoo fores, dahoo dores (ph) - welcome, welcome Christmas - Christmas Day.
NPR transcripts are created on a rush deadline by Verb8tm, Inc., an NPR contractor, and produced using a proprietary transcription process developed with NPR. This text may not be in its final form and may be updated or revised in the future. Accuracy and availability may vary. The authoritative record of NPR’s programming is the audio record.