Acts 4 has two references to heaven, and neither opens up new vistas for us on the meaning of heaven.
Acts 4:12: There is salvation in no one else, for there is no other name under heaven given among mortals by which we must be saved.
Acts 4:24: When they heard it, they raised their voices together to God and said, ?Sovereign Lord, who made the heaven and the earth, the sea, and everything in them, 25 it is you who said by the Holy Spirit through our ancestor David, your servant …
In general, “heaven” here refers to the abode of God, the beyond-ness where God dwells and where God’s will rules supreme. It also refers to the skies and what is up (heaven) and what is down (earth) is the creation of God.
I would not want to rule out of court a possible allusion to Isa 45:22-25 in Acts 4:12:
22 Turn to me and be saved,
all the ends of the earth!
For I am God, and there is no other.
23 By myself I have sworn,
from my mouth has gone forth in righteousness
a word that shall not return:
?To me every knee shall bow,
every tongue shall swear.?
24 Only in the LORD, it shall be said of me,
are righteousness and strength;
all who were incensed against him
shall come to him and be ashamed.
25 In the LORD all the offspring of Israel
shall triumph and glory.