31 The word רְוָחָה (révakhah) means “respite, relief.” 926 relates it to the verb רָוַח (ravakh, “to be wide, spacious”). There would be relief when there was freedom to move about.
32 וְהַכְבֵּד (véhakhbed) is a Hiphil infinitive absolute, functioning as a finite verb. The meaning of the word is “to make heavy,” and so stubborn, sluggish, indifferent. It summarizes his attitude and the outcome, that he refused to keep his promises.
33 The end of the plague revealed clearly God’s absolute control over Egypt’s life and deities—all at the power of the man who prayed to God. Yahweh had made life unpleasant for the people by sending the plague, but he was also the one who could remove it. The only recourse anyone has in such trouble is to pray to the sovereign Lord God. Everyone should know that there is no one like Yahweh.

In other versions

But when Pharaoh saw that there was a respite, he hardened his heart and would not listen to them, as the Lord had said.

But when Pharaoh saw that there was relief, he hardened his heart and would not listen to Moses and Aaron, just as the Lord had said.

But when Pharaoh saw there was relief, he hardened his heart and would not listen to them, as the Lord had said.

But when Pharaoh saw that relief had come, he became stubborn. He refused to listen to Moses and Aaron, just as the Lord had predicted.

And Pharaoh saw that there was relief, and he made his heart insensitive, and he did not listen to them, as Yahweh had spoken.

But when Pharaoh saw that there was respite, he hardened his heart, and hearkened not unto them; as the Lord had said.

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