**Core Concept**
The patient is experiencing opioid overdose, characterized by respiratory depression, bradycardia, constricted pupils, and hypotension. The body's compensatory mechanisms are attempting to counteract the opioid's effects, as evident from the brisk bilateral deep tendon reflexes.

**Why the Correct Answer is Right**
The administration of naloxone is the best treatment for opioid overdose. Naloxone is an opioid antagonist that rapidly reverses opioid-induced respiratory depression by competitively binding to opioid receptors in the brain, specifically the mu-receptors. This action counteracts the effects of heroin, allowing for the restoration of normal breathing and cardiovascular function. The dose of naloxone should ideally be titrated to avoid precipitating opioid withdrawal symptoms.

**Why Each Wrong Option is Incorrect**
**Option A:**
Administering a benzodiazepine would worsen the patient's respiratory depression, as benzodiazepines enhance the effects of opioids on the central nervous system.

**Option B:**
Using a beta-agonist would not address the underlying cause of the patient's symptoms and may even worsen cardiovascular instability.

**Option C:**
Administering a calcium channel blocker would be contraindicated in this scenario, as the patient's cardiovascular system is already compromised.

**Option D:**
Using a parasympatholytic agent would not be effective in treating opioid overdose and may even worsen bradycardia.

**Clinical Pearl / High-Yield Fact**
It's essential to note that naloxone has a shorter half-life than most opioids, so repeated doses may be necessary to maintain efficacy. Additionally, patients who have been using opioids for an extended period may require higher doses of naloxone to achieve a response.

**Correct Answer:** C. Administering naloxone.