Yes, Virginia, some atheists go to Heaven. The path to Heaven is easiest for believing and practicing Catholics. Our path to Heaven is level, wide, and well-lit. We have many helps along that path, and the company and assistance of Saints and Angels. Then the path to Heaven for atheists is rocky, uneven, and dark. They have few helps because they have turned away from the benefits offered by belief in God, by Christianity, and by Catholicism. But they can die in the state of grace, and, after a long time in Purgatory, arrive at eternal life in Heaven.
To be saved, an atheist must first enter the state of grace. Many atheists in Western society were baptized as infants or children, since they grew up in Christian families. Other atheists can enter the state of grace by an implicit baptism of desire. And the essential nature of this baptism of desire, for those who do not believe in God, is the love of neighbor. By sincerely and selflessly loving others, the atheist (or any other non-baptized person) also implicitly loves God. We are made in the image of God, and all that is in us, which is worthy of being loved, is from God. So by an act of love, the atheist can enter the state of grace.
The state of grace is only lost by the commission of an actual mortal sin. If a Catholic commits an actual mortal sin, he or she can return to the state of grace by at least imperfect contrition and Confession. But non-believers, and believers who lack the Sacrament of Confession, must repent with perfect contrition to return to the state of grace.
This perfect contrition is usually found in sorrow for sins out of love for God. But since the love of neighbor always includes, at least implicitly, the love of God, a person can repent out of love for his neighbor, who is harmed by his sins, and thereby achieve perfect contrition. An act of perfect contrition can also be implicit. The person might, after committing an actual mortal sin, express true selfless love of other persons. This love implicitly includes repentance from every grave sin. For sin and love are opposed to one another. So by subsequently loving others selflessly, the person cooperates with grace so fully as to return to the state of grace, by implicit perfect contrition.
Is not the rejection of belief in God itself an actual mortal sin? Not necessarily. It is always at least an objective mortal sin. But if the person rejects religion and belief in God with a sincere but mistaken conscience, he is not condemned to Hell for that sin. It is objectively grave, but does not include the full culpability of actual mortal sin.
In this way, an atheist can enter the state of grace, return to the state of grace after actual mortal sin, and die in a state of grace so as to be saved. But, in all likelihood, not having prayed, fasted, or practiced any religious devotions, not having worshiped God, nor loved Him explicitly, the atheist who dies in the state of grace will have to spend a long time in Purgatory.
Ronald L. Conte Jr.
Roman Catholic theologian