Some believe heaven and hell are in the mind and only empty stillness exists when you die. These people believe that suicide would only be a gate into that empty stillness.
Others believe there is a literal heaven and a literal hell. The greatest number of these people base their beliefs on a belief in God. A large number of these people believe if one commits suicide, their destination will be hell.
Ultimately, you have to search for the answer within yourself, remembering that there is no going back once the act is done and that there is no one who can say there definitely is not a heaven and hell.