Heart Donor

This is a famous Spanish-language horror/webcomic short story called “Kevin & Clore” (sometimes shared under titles like “El trasplante” or “Un amor eterno”). It’s a classic twist-ending urban legend told in comic form.
Here is the full story explained panel by panel (spoiler-heavy, obviously):

A young woman named Clore dies in an accident (we see her body parts scattered).
Her boyfriend Kevin is dying and needs a heart transplant.
Clore is an organ donor. Her heart is given to Kevin, saving his life.
Kevin recovers, leaves the hospital, and begins a happy new life.
Time passes. Kevin meets a new girl (blonde, cheerful, beauty mark on her cheek) and falls in love again.
They get married, go on dates, have a normal happy relationship. Kevin seems to have completely moved on.
One night Kevin wakes up terrified from a nightmare, sweating.
Later he catches his new wife cheating on him with another man (in a cemetery, no less).
He’s heartbroken again.
But then we see the new wife in the hospital, dying, with an oxygen tube, laughing maniacally while Kevin and the doctor celebrate.
Final newspaper headline: “Couple donates heart after death… patients who received a heart transplant…”

The twist:
The “new wife” was actually Clore’s heart controlling Kevin’s new girlfriend’s body. After Kevin moved on and started loving someone else, Clore’s heart became jealous/possessive and basically killed its new host from the inside (or drove her insane) so it could “be with Kevin forever” in death. In the end both Kevin and the new girlfriend die, and their hearts are harvested… meaning Clore’s heart will be transplanted into yet another person Kevin might love in the future.
The last line reads:
“A love that lasts beyond death. Although people may change, their hearts remain eternally united.”
It’s a darkly ironic, body-horror love story: Clore’s love was so intense that even in death her heart refuses to let Kevin love anyone else, and will keep killing his partners until the end of time.
Very creepy, very popular in Spanish-speaking internet horror circles!