Science fiction is what it says on the tin. Fiction based around Science.
Doctor Who is very science fiction. Heroes isn't really based around science but it is highly fictional. The only way you could say Heroes is science is biological, since they are not normal humans.
I love Doctor Who, and I got to meet David Tennant for five minutes since my maths teacher was his best friend when they were wee. He doesn't even act on Doctor Who, that's him basically being himself :P