Pharaoh sent officials and found that none of the livestock of the Israelites had died. But Pharaoh's heart was hardened, and he would not let the people go.

Exodus 7:13
Still, Pharaoh's heart was hardened, and he would not listen to them, just as the LORD had said.

Exodus 7:14
Then the LORD said to Moses, "Pharaoh's heart is unyielding; he refuses to let the people go.

Exodus 8:32
But Pharaoh hardened his heart this time as well, and he would not let the people go.

Exodus 9:8
Then the LORD said to Moses and Aaron, "Take handfuls of soot from the furnace; in the sight of Pharaoh, Moses is to toss it into the air.

And Pharaoh sent, and, behold, there was not one of the cattle of the Israelites dead. And the heart of Pharaoh was hardened, and he did not let the people go.