וַיֹּ֤אמֶר יְהוָה֙ אֶל־מֹשֶׁ֔ה כָּבֵ֖ד לֵ֣ב פַּרְעֹ֑ה מֵאֵ֖ן לְשַׁלַּ֥ח הָעָֽם׃
And the LORD said unto Moses: ‘Pharaoh’s heart is stubborn, he refuseth to let the people go.
Targum Jonathan on Exodus
And the Lord said to Mosheh, The disposition of Pharoh's heart is obdurated in refusing to release the people.