According to Scripture, Enoch and Elijah may have been assumed into heaven before the time of Christ. This is less clear in Enoch's case, since Genesis 5:24 says only that God "took" him, but doesn't say where. Sirach 44:16 and 49:14 make it clear that he was taken up from the earth, and Hebrews 11:5 adds "so that he should not see death."
In Elijah's case, 2 Kings 2:11 states that "Elijah went up by a whirlwind into heaven." First Maccabees 2:58 adds, "Elijah because of great zeal for the Law was taken up into heaven. " Taken at face value, these would seem to indicate that both Enoch and Elijah were assumed into heaven. But the Church teaches that heaven was not yet opened to the saints because Christ had not yet come. How can this be explained?
One possible explanation is to say that they didn't really go to heaven but to the abode of the dead where the souls of the righteous were waiting for the Messiah to open heaven. A difficulty is that the abode of the dead, or she'ol, is pictured in the Old Testament as being down (e.g., Nm 16:33 speaks of Korah and his followers going "down alive into she'ol"), yet Enoch and Elijah are depicted as being taken up.
Another possibility would be to say they were taken up but to a different kind of heaven than the one Christ opened. Or it is possible to say simply that they received entrance to heaven as a grace which came from the redemption Christ wrought – only they received it early, as did Mary when she was immaculately conceived. Like Mary, Enoch and Elijah may have been foretastes of the good things to come. In such a case, they would be exceptions to the rule. But God can do what he wants.