There are no descriptions in the Bible of guards at the gates of heaven. All those jokes about Paul or Peter standing at the pearly gates are not true. There are pearly gates:
The 12 gates were made from 12 pearls. Each gate was made out of a single pearl. The main street of the city was made out of pure gold, as clear as glass. Revelation 21:12
These gates lead into the heavenly city where God dwells. No need for guards since that would mean the presence of evil lives some where on the outside and threatens to invade at some point. No such threat of evil will ever exist in heaven.