Final answer:
The nurse should plan to administer naloxone to the client.
Step-by-step explanation:
The nurse should plan to administer naloxone to the client who has heroin toxicity. Naloxone is an opioid antagonist, meaning it blocks the effects of opioids by competing for the same receptors in the brain. It can reverse the respiratory depression caused by opioids and help the client regain consciousness and normal breathing.