Since Valentine's Day just recently ended, I suppose it would be appropriate to talk about hearts. And since this is an Oz post, I'm sure the first subject to come to anyone's mind would be the Tin Woodman, who sought one for his tin body from the Wizard of Oz. The Wizard had no magical powers at this point, but he still provided Nick Chopper with a plush heart stuffed with sawdust, and his friend the Scarecrow with brains made of bran mixed with pins and needles. The story makes it clear that the Tin Woodman and the Scarecrow, respectively, were already kind-hearted and intelligent, but they needed the symbols to be satisfied. In Tin Woodman, Nick explains that his heart is kind rather than loving as an excuse for not having sought out Nimmie Amee, the girl he had planned to marry before his series of axidents. Really, though, I think it's just that, what with his new life and new friends, he really no longer had any interest in Nimmie Amee. He is certainly capable of showing love, even if he claims he isn't.
Some of the later Oz books also play with the idea of hearts and brains. Jack Pumpkinhead uses the seeds in his pumpkins for brains, and while he's hardly the brightest man in Oz, he has occasional flashes of insight. Dr. Pipt gave the Glass Cat brains of shiny pink stones that made her conceited, and a ruby heart that wasn't very compassionate. The Wizard temporarily made her more humble by giving her transparent brains at the end of Patchwork Girl, but she has the pink ones back again in Magic. By the time he brings the Patchwork Girl to life, Pipt seems to have improved on his brain-making abilities, with a set of powders that each provide a particular trait used for her brains. In Tik-Tok, the Great Jinjin Tititi-Hoochoo is said to have no heart, so that emotion and compassion will not interfere with his justice. Moving on to Ruth Plumly Thompson's books, the reanimated Terrybubble seems to function just fine without physical brains or a heart, but he does prefer to keep Speedy in his chest where his heart once was. When dealing with such matters, it's not entirely clear whether the presence or absence of hearts and brains really impact these characters, or they just think they do. In the end, though, I guess it amounts to about the same thing.