A.T. Robertson Commentary Acts 8:6

"And the multitudes gave heed with one accord unto the things that were spoken by Philip, when they heard, and saw the signs which he did." — Acts 8:6 (ASV)

Gave heed (προσειχον). Imperfect active as in verses 10,11, there with dative of the person (αυτω), here with the dative of the thing (τοις λεγομενοις). There is an ellipse of νουν (mind). They kept on giving heed or holding the mind on the things said by Philip, spell-bound, in a word.

When they heard (εν τω ακουειν αυτους). Favourite Lukan idiom, εν and the locative case of the articlar infinitive with the accusative of general reference "in the hearing as to them."

Which he did (α εποιε). Imperfect active again, which he kept on doing from time to time. Philip wrought real miracles which upset the schemes of Simon Magus.