Also, I have linked my moral values to the will of God. So what is morally good is also what God wants (by definition this is: I define the will of God as morally good). Therefore an atheist who does good things is doing God will (again, by definition). Doing Gods will is doing good and doing good does not depend on what you believe, but on your actions.
About repentance, I think most humans have a weak for people who regret everything they've done.. If people have done harm to you, but they regret everything.. they are disgust by their own actions.. They ask you to forgive them while crying

And again, I have linked good to God.. so if forgiving them is good, than it is also what God wants (as our moral values are based on him). So then it would make sense that those who really really regret what they have done (and wanna do good from now on), will also 'go to heaven'. (Quotations here because the Bible itself doesn't talk about going to heaven, it only reports on a new heaven and new earth in the end of times. But that's another discussion
