Acts 16.14 is interesting because "the Lord opened Lydia's heart to respond to the things spoken by Paul". So far the consensus exposition of "God changing our heart" seems to be that "we change our heart by reading God's word" or similar. I find it hard to read that sort of process into Acts 16.14. The process in Acts is that God works on our heart so that we come to respond to his word. We might read God's word all our lives and not respond.
"The Lord opened Lydia's heart" could mean anything. It could mean she had been encouraged by reading the Scriptures. It could mean she had experienced the mercy of God. It could mean something had happened in her life to make her think about things. We don't know.