Here "heart" refers to Pharaoh. His stubborn attitude is spoken of as if his heart was hard. See how you translated this in [Exodus 7:13](./11.md). AT: "Pharaoh is stubborn" (See: [[rc://en/ta/man/translate/figs-synecdoche]] and [[rc://en/ta/man/translate/figs-metaphor]])
The full meaning of this statement can be made explicit. AT: "when he goes down to the Nile River to bathe" (See: [[rc://en/ta/man/translate/figs-explicit]])