Which knoweth the heart (kardiognōstēs). Late word from kardia (heart) and gnōstēs (known, ginōskō). In the N.T. only here and Act 1:24 which see.
Giving them the Holy Spirit (dous to pneuma to hagion). And before their baptism. This was the Lord’s doing. They had accepted (Act 11:18) this witness of God then and it was true now of these other Gentile converts.