Here the "heart" represents a person's thoughts and true feelings. AT: "my thoughts" or "my inner feelings" (See: [[rc://en/ta/man/translate/figs-metonymy]])
Here Jeremiah asks Yahweh to prepare to punish the wicked as if they were sheep to be taken away to be slaughtered. AT: "Take the wicked people away, like sheep for slaughter" or "Prepare to punish those wicked people" (See: [[rc://en/ta/man/translate/figs-metaphor]])
This can be stated in active form. AT: "The animals and the birds are gone" or "The animals and the birds have all died" (See: [[rc://en/ta/man/translate/figs-activepassive]])
Possible meanings are 1) The people are saying that God does not know what things will happen to them in their future or 2) God is unaware of their sin. AT: "God does not see the sinful things that we do"