The phrase after this (meta tauta in Greek) is repeated twice in (Revelation 4:1). The Bible has other important references to heaven, in passages such as (Isaiah 6:1-8) (Ezekiel 1), and in passages describing the Tabernacle, which symbolically describes heaven (Exodus 25-32) (Exodus 35-40).
After these things I looked, and behold, a door standing open in heaven. And the first voice which I heard was like a trumpet speaking with me, saying, “Come up here, and I will show you things which must take place after this.”
After these things. After …