An atheist does not believe in a Hell or other afterlife. Assuming this opinion is correct, an atheist does not go to Heaven/Hell after death - and neither does anyone else.
Theists believe in an afterlife. Some (like Christians, Jews and Moslems) believe in a Heaven and Hell, others believe in a continuing series of rebirths leading to some sort of reward.
For theists that believe in a Heaven/Hell there is an imposing list of does and don'ts that the believer has to comply with to "succeed". Most Heavens are exclusive to their particular sect's beliefs. These groups would see the majority of the human race going to Hell, atheists included.