Is there a spell or a sword or whatever that...

...wounds you and slowly kills you until you die shortly after you were wounded? Okay, if that doesn't make any sense, let me explain:
I want to write a fanfiction, on which one of the characters gets wounded in the final battle. The person who gets wounded has to die like 5 minutes later, and she has to be impossible to heal. Is there a poison or a spell or a sword or something in that region that'll do that to the character?