From Heroes Wiki
Matt's nose bleeds when he strains to read the mind of the Haitian.
A nosebleed sometimes occurs when evolved humans strain to use their abilities beyond their normal limits. Nosebleeds can also happen in both humans and evolved humans when they attempt to resist telepathic abilities.
Against the advice of Ando and Mohinder Suresh, Hiro continues to use his power, only to eventually experience worsening symptoms, including bleeding from his left ear, blood within his left eyeball, and loss of consciousness.
Hiro suffers a nosebleed after successfully traveling eight weeks back into the past, to save a film. When he arrives, he finds Mohinder just about to burn the film, and wipes the blood off his nose before saving the film.
- In the alternate ending to Season Two, Matt Parkman's nose bleeds when over-exerting his power to send messages to the entire police station.
- Two other bleeding examples when power overloading from other body parts are: Matt Neuenberg bleeding from the ears when using his ability to download the Primatech computer banks in (The End of Hana and Drucker), and Hana Gitelman when bleeding from the nose, eyes, and mouth after being attacked by a computer virus while communicating with a satellite in (The Death of Hana Gitelman, Part 2).