Heart Trauma

"Someday I'll meet someone
Whose heart joins with mine
Aortas and arteries all intertwined
They'll beat so much stronger
Than they could apart
Eight chambers of muscle to hustle
The love in our heart"

—Urinetown

When a character has something physically happen to their heart (often in a way that generally would be impossible without magic being involved), it often affects their personality in drastic ways. Either they lose all of their emotions, or their personality changes—for the worse. Seen most often in fantasy works, particularly those with a symbolic or Fairy Tale theme.

This trope differs from The Heartless in that while those characters are simply composed of negative emotions (which might not actually be related to their hearts), these characters sometimes literally lose their hearts.

Compare Soul Jar, where the thing done to the heart affects their vulnerability, and Literal Change of Heart, which involves replacing a missing or damaged heart.

Examples of Heart Trauma include:

Anime and Manga

In Princess Tutu, Prince Siegfried uses a "forbidden spell" to shatter his heart, which is then used to seal away the Raven (who is the Big Bad of his fairytale). Without it, he's an Extreme Doormat who does whatever anyone suggests and is unable to express emotions or opinions. The Magical Girl named in the title has the task to restore his heart, one piece at a time.
- In the second season the Prince's heart is tainted by the Raven's blood, which causes him to become evil and serve the Raven. Toward the end of the season he turns into a crow and is only saved from giving his life to the Raven by The Power of Love coming from the Dark Magical Girl, who has to pull out an Heroic Sacrifice to make herself heard.
The Hollows in Bleach, who have developed a big hole in their chest where their heart ought to be, as a not-so-subtle symbol of their heartlessness.
In Towa Kamo Shirenai, Kosumo has a very weak heart, which she describes as "a defective product". She has a near fatal seizure and must get a transplant... and it happens. Then, the heart that was given to her turned out to belong to a Miko and Magical Girl Warrior...
Tsubaki from Yami no Matsuei also got a heart transplant due to hers being too weak. It belonged to her best friend Eileen, who was kidnapped and killed for it. She came to learn about it and was so emotionally crushed that she developed a Split Personality that called herself "Eileen" and started killing people.
In Gankutsuou, the Count of Monte Cristo underwent a treatment that makes him invulnerable to injury at the same time he devoted himself to vengeance. The point is made that his heart is now both metaphorically and literally cold and hard.
In Howl's Moving Castle Howl is literally heartless because of a Deal with the Devil.He gets better eventually.
Anju Kitahara from the Marmalade Boy anime series is an Ill Girl with a weak heart, and suffers an almost fatal seizure in Christmas. After this she gets Put on a Bus, and when she comes back to Japan it's revealed that she was operated and has gotten better.

Comic Books

Tony Stark becomes Iron Man after sustaining a nearly fatal chest wound. Tony implants himself with a powerful reactor which prevents deadly shrapnel from reaching his heart; this very reactor later powers his suit. To be fair, the radical change in his outlook on life is primarily due to his newly gained first-hand knowledge of the horrors of war, as opposed to the changes in his cardiovascular system.
The Marvel Comics villain Master Pandemonium has a star-shaped hole in his chest where his heart (and supposedly his soul) used to be, after he makes a life-saving Deal with the Devil. Turns out the soul fragments he's been reclaiming aren't actually his, however.
X-Men doesn't usually fail biology forever to quite this extreme, but The Stepford Cuckoos were forced to keep their hearts in diamond form all the time to contain the Phoenix fragment within them, resulting in loss of emotions (instead of the more probable effect of loss of life.)
In Nightmares & Fairy Tales, one chapter centers around a retelling of the fairy tale of Snow White. In it the Queen has Snow White's heart cut out, then she cuts out her own heart and puts Snow's in her chest. This is done because she is told that outer beauty is reflected by the heart. While it does work and she becomes beautiful, it leaves poor Snow White with no heart, wandering aimlessly through the forest. She temporarily replaces her heart with an apple and later hunts down the Queen, rips out her own heart, and puts it back, leaving Snow healthy and beautiful and the Queen heartless, weak, and hideous.

Fan Works

Done by the Skull Kid in The Blue Blur of Termina, when he rips out Lady Venus's heart in an attempt to kill her.

Film

In Pirates of the Caribbean: Dead Man's Chest, Davy Jones is said to have cut out his heart and hid it partially so he could stop the pain he felt from his lover's betrayal.
In Dragonheart, future king Einon is given a piece of the heart of a dragon to save his life. While he'd actually been a bit of a bastard from the start, the invincibility which sharing Draco's life grants him leaves Einon free to act up a lot more than he might've dared, had he remained an ordinary mortal.

Literature

In Hans Christian Andersen's Fairy Tale "The Snow Queen", a boy named Kai has a piece of a mirror that shows a negative view of the world pierce his heart, which causes him to become cold and distant towards his childhood friend Gerda, before he's taken away by the Snow Queen. Gerda goes on a journey to find him and eventually rescues Kai, again through The Power of Love. (It's possible the second-season Princess Tutu example was a reference to this fairytale.)
In The Grinch Who Stole Christmas, the Narrator guesses that the Grinch might be nasty and hate Christmas because his heart is "two sizes too small". When the Grinch learns the Aesop about what Christmas is all about, his heart grows "three sizes larger" and he becomes a lovable, kindhearted, heroic figure.
- The Grinch example was pastiched on South Park. "And what happened next? Well, in South Park, they say Johnny Cochrane's small heart grew three sizes that day!"
In Howl's Moving Castle Howl is literally heartless because of a Deal with the Devil. He gets better eventually.
Tom from Mortal Engines has a wound in his heart from being shot by Pennyroyal; it weighs heavily on his mind and makes him weaker and weaker over the course of the third and fourth books, eventually killing him at the climax of the fourth.
One of the tales of Tales Of Beedle The Bard, a supplemental book to the Harry Potter series, is "The Warlock's Hairy Heart", where the title warlock removes his own heart in order not to fall prey to the "foolishness" of love.
In one of the Doctor Who Tie In Novels, one of the Doctor's hearts is stolen. While he's awake. Normally he'd be dead; as it is he's still capable of putting some serious effort towards saving the world again, sleeps for a week, and is quietly traumatized and has Bad Dreams. It also makes him more like a regular old human being. Also, the fact his heart has been transplanted to someone else results in some kind of weird Soul Jar arrangement, where if one of them is hurt, it hurts the other, but neither can be seriously harmed as long as the other is okay. Resulting in the Doctor walking around clinically dead for a while, poor thing. He eventually grows a new one.
The Tin Woodsman from The Wonderful Wizard of Oz is entirely convinced he falls under this trope. He doesn't -- in fact, he's very nearly The Messiah, endeavoring to be kind to all living things so that he doesn't do anything horrible without a heart to guide him.
In Everworld, the dragon Nidhoggr magically replaces the protagonists' hearts with rubies from his Treasure Room, informing them that they'll die after six days unless he gives them their real hearts back. He does not, however, take the heart of Token Evil Teammate Senna; David notes that if he knew the reason why, it would "terrify" him. In reality, it's because witches have "hard hearts," and Niddhogr was too cheap to waste a diamond.

Live-Action TV

An episode of Angel concerned a vampire that removed his heart surgically so that Angel would be unable to stake him. His heart being removed was symbolic of the fact that Angel was responsible for the death of his lover. His final comment, when he eventually runs out of steam, at least left an impression, since it was directed at Angel, and his well-known curse never to know the greatest joy. "I lived. You just existed."
Captain Picard of Star Trek: The Next Generation fame had a Wonderful Life episode about the incident that resulted in his having to have his original heart replaced with a mechanical one. The episode had Q give Picard the chance to go back to his youth and prevent the fight where he was stabbed through the heart. He avoids the fight and his future is changed. Instead of being Captain, he is just a lowly science officer who never takes any risks, always plays it safe, and leads a boring, mundane life. Realizing that it was his near-death experience that made him appreciate life and taught him to live life to the fullest even if means taking risks, he begs Q to take him back to the fight in his youth again. This time, he goes through with the fight, and as he is laying on the ground with a knife through his heart, he realizes this event is what makes him the man that he is.

Theater

A possible example in the musical of Wicked: Elphaba's sister Nessarose is in love with a Munchkin named Boq, who in turn is in love with Glinda. Nessarose steals the Grimmorie (a book of extremely powerful, irreversible, arcane magic) from Elphaba and tries to cast a spell that will make Boq's heart belong to her. It fails: she ends up destroying his heart. The only thing Elphaba can do to save Boq is turn him into a tin golem, so that he doesn't need a heart.
Prince Trevor Amongst the Elephants has the titular character's heart taken for offending The Three Graces.

Tabletop Games

In the Polish fantasy-steampunk RPG Wolsung, the dwarves value logic over emotions and often implant magitek prosthetics into their bodies. If they overdo with the implants, they turn into uhrwerk - "clockwork dwarves", completely and irreversibly losing their emotions and, to a slightly lesser extent, morality. Heart replacement is the most common reason for becoming uhrwerk.

Video Games

Although this trope is different from The Heartless, the Nobodies from Kingdom Hearts II are still a good example of this trope. They are the shell left behind when a Heartless steals a person's heart. Apparently, losing your heart gives you superpowers and a taste for black robes. They say they can feel no emotion, although there's some debate in the fandom about whether or not that's true. At the very least, they lack empathy.
- To be even more specific: When one becomes a Nobody, their body changes. The human Nobodies in the Organization are the cream of the crop, people who had such a strong will to live when they lost their heart that their "shell" barely changed appearance, so they look pretty similar to their old selves. Everyone else with a weaker heart deforms into a clothing-like, vaguely humanoid lesser Nobody.
The Shadow Pokémon in Colosseum and XD Gale of Darkness have their hearts sealed off by the bad guys, which prevents them from leveling up, gives them different moves and causes them to go into a periodic self-injurious state similar to Confusion. Forming an emotional bond with the Pokemon is required (but not sufficient) to cure them.
The driving force behind male lead Hisao Nakai's character development in Katawa Shoujo is his diagnosis of congenital arrythmia, a heart condition that could kill him at any time. This diagnosis results in his transfer to a new school (thus the plot of the game) and also forces him to look at himself and his life.
- In the April's Fools Prank from 2011, one of the prospect "new girls" was Rika Katayama, a young girl with hypoplastic left heart syndrome. Unlike Hisao, Rika was diagnosed early in her life and thus she has been in and out of treatments for years already.

Western Animation

The animated TV series based on Disney's Aladdin had an episode where Aladdin's head is magically separated from his body. The head and the body both survive as independent beings, but without the influence of his heart Aladdin's head becomes logical and emotionless. Meanwhile, his body without the head's influence becomes headstrong and impulsive. And clumsy.
Mildly subverted, in the first episode of Silverhawks Steelwill's and Steelheart's hearts fail while they're being cyborgized and are replaced with mechanical ones. The doctor then points the appropriateness of their names. However they seem unaffected (possibly the only bit of good science in the series).
Hefty in The Smurfs goes through some heart trouble when a flea carrying Gargamel's hate juice bites him and causes his heart tattoo to change into a yellow X, also changing Hefty into a hateful abusive Smurf. Near the end of the story, when Hefty sees that Papa Smurf is being threatened by Gargamel, his true natured self and his heart tattoo return just in time for Hefty to rescue Papa Smurf.