“unyielding.” The Hebrew word is kabad (#03513 כָּבַד), meaning unyielding, hard, insensitive, stubborn, unresponsive, dull. Pharaoh’s heart was hard and unresponsive to God’s request, insensitive to both the Israelites and Egyptians, and dull such that it could not see where his refusal of God’s request would lead. See commentary on Exodus 4:21.