But is only the conjunction waw, but in translation the context may demand a stronger transitional marker such as “In spite of all that.” The LORD is Yahweh, and it is very clear that Yahweh is the one who hardened the heart of Pharaoh. Literally “Yahweh made strong the heart of Pharaoh.” (So New Jewish Publication Society’s Tanakh has “the LORD stiffened the heart of Pharaoh.”) This means that he “made the king stubborn” (Good News Translation), or “obstinate” (New English Bible, New American Bible). (See the discussion at 4.21 and 7.13.)

And he did not listen to them may be understood as “he refused to listen to them” (Jerusalem Bible) or “he would not heed them” (New Jewish Publication Society’s Tanakh). This refers back to the demand to “let my people go” in 9.1, even though the account of this plague does not include it. But it also refers back to 7.3-4, where Yahweh predicted that he would “harden Pharaoh’s heart” so that he “would not listen to Moses and Aaron.”

Quoted with permission from Osborn, Noel D. and Hatton, Howard A. A Handbook on Exodus. (UBS Helps for Translators). New York: UBS, 1999. For this and other handbooks for translators see here .