Did God make Pharaoh harden his heart, or did Pharaoh harden his own heart?
Pharaoh hardened his own heart. God did not force him to do so; God placed him in a position to accept or reject, and Pharaoh rejected, thereby hardening himself. Scripture also speaks of God hardening, but the context clarifies that hardening follows lostness rather than causing it.
Les explains that the word "hardeneth" in Scripture is often translated "heavy." As Pharaoh opposed God, the weight of God's wrath weighed down on him. Pharaoh, like anyone today, came to the place of hardening his own heart, not because God made him do it, but because God put him in a place of either accepting or rejecting, and by rejecting he hardened his own heart. Even though Scripture says God hardened, Les cites the quote: "Men are not lost because they are hardened. They are hardened because they are lost."
Therefore hath he mercy on whom he will have mercy, and whom he will he hardeneth.