The "heart" refers to the whole person, emphasizing their emotions and desires. Alternate translation: "They are deceitful" (See: [[rc://en/ta/man/translate/figs-synecdoche]])
Here "guilt" is a metonym for the punishment that is associated with it. This punishment is spoken of as if it was a heavy load for them to carry. Alternate translation: "now is the time that Yahweh will punish them for their sins" (See: [[rc://en/ta/man/translate/figs-metonymy]] and [[rc://en/ta/man/translate/figs-metaphor]])