There do seem to have been some shenanigans. A hoax press release was sent, announcing his defeat, but was found to originate in Virgina, USA, rather than Venezuela. More details here.
"There are also reports coming in of phony election results being broadcast on Venezuelan television, and rigged exit polls organized by the very people who supported an unsuccessful coup against Chavez in 2002 -- an organization funded by the US government through the National Endowment for Democracy. Your tax dollars at work
This is the eighth time Mr Chavez's mandate as leader has been approved since 1998, after two presidential elections and six referendums. So back off, Bush.