9e7742db_ime_manipulation___Heroes_Wiki__Theory
[Citations] Arnold died of a tumor and Hiro has been diagnosed with one. [Notes] • Samuel states that "his [Arnold's] body couldn't take the strain". (Once Upon a Time in Texas) - Arnold was murdered by Samuel. (Bloodlines, Part 2) - Hiro got the tumor before he could time travel again. - Masi Oka said in an interview that Hiro got the tumor because he took others into frozen time, which overloaded his brain. • Maybe Arnold also did that. • Neither Arthur Petrelli nor Peter Petrelli showed signs of a tumor, and Future Hiro seemed perfectly healthy. This could be because neither Arthur nor Peter used time traveling as extensively as Hiro. [Theory] 
Travel through time eventually causes a fatal brain tumor.
Theory:Space-time manipulation - Heroes Wiki
Theory