Here "heart" refers to Pharaoh. His stubborn attitude is spoken of as if his heart was hard. See how you translated this in [Exodus 4:21](../04/21.md). Alternate translation: "will cause Pharaoh to be stubborn" (See: [[rc://en/ta/man/jit/figs-synecdoche]] and [[rc://en/ta/man/jit/figs-metaphor]])
The words "signs" and "wonders" mean basically the same thing. God uses them to emphasize the greatness of what he will do in Egypt. (See: [[rc://en/ta/man/jit/figs-doublet]])