I've been in contact for some time now with a fellow Christian. He frequently uses phrases like "the Lord spoke to me" and "the Lord put this on my heart." He comes across like he believes he is receiving direct messages from God outside of Scripture. To me, this doesn't seem to gel with what we read in Hebrews 1:1-2 - "In the past God spoke to our forefathers through the prophets at many times and in various ways, but in these last days he has spoken to us by his Son, whom he appointed heir of all things, and through whom he made the universe." I've always understood that passage to mean (and have been taught as such) that we shouldn't expect direct revelation from God anymore, and we should only look to Scripture for God's answers to questions we might have. What's the best way to respond to someone who insists on saying that "the Lord spoke to me" or "the Lord put this on my heart?"
God of course can do anything. He can communicate to us any way he wants. The Bible describes instances when God did speak directly to people, through others and in dreams. The fact that God communicated in these ways in the past does not guarantee that God will do so in the future. We have no promise of God communicating to us beyond Scripture.
Hebrews 1:1-2, as you indicated, teaches that we have God’s full communication to us in the pages of the Old and New Testament. There is no need to look elsewhere for communication from God.
If there is a “voice” from God inside us, it is the natural knowledge of his law and a conscience that is guided properly by Holy Scripture. If there is a “voice” from God inside us, it is the new self—that part of us that is “created to be like God in true righteousness and holiness” (Ephesians 4:24)—that desires to live life according to God’s will.
It could be that your friend recalls or thinks of Bible verses at times. When he does that, he refers to the Lord speaking to him or putting something on his heart. That “speaking” is the recollection and application of God’s word.
Your question is a good reminder that we do well to focus on God’s communication to us through the Bible—and our communication to him in prayer.