Okay, let's tackle this question. The patient is on metoprolol, which is a beta-blocker, and then given verapamil. The question is about the effect of combining these two drugs.

First, I need to recall the mechanisms of action for both drugs. Metoprolol is a beta-1 selective blocker, so it reduces heart rate and cardiac output. Verapamil is a calcium channel blocker, specifically a non-dihydropyridine type, which affects the heart by decreasing conduction through the AV node and reducing heart rate and contractility.

When combined, both drugs can slow the heart rate. Beta-blockers reduce sympathetic stimulation, while calcium channel blockers like verapamil inhibit calcium influx, which is crucial for AV node conduction. So together, they might have an additive effect on slowing the heart rate. This could lead to bradycardia or even heart block, especially in patients with pre-existing conduction issues.

Now, looking at the options, the correct answer would be something like "Additive negative chronotropic effect". The other options might include things like increased blood pressure, which is unlikely, or increased cardiac output, which is the opposite. I need to make sure each wrong option is addressed properly. For example, if an option says "Increased heart rate", that's wrong because both drugs lower heart rate. Another wrong option could be "No effect on heart rate", which is incorrect because the combination does affect heart rate.

The clinical pearl here is that combining beta-blockers and calcium channel blockers (especially verapamil or diltiazem) can lead to significant bradycardia and should be used cautiously, particularly in patients with underlying heart conditions. This combination is sometimes used in specific cases like hypertension or angina, but requires close monitoring.

So the correct answer is the additive effect on heart rate reduction. The explanation should detail the mechanisms of each drug and their combined effect. The incorrect options are wrong because they don't align with the pharmacological actions of the drugs involved.

**Core Concept**
This question tests the pharmacological interaction between beta-blockers (metoprolol) and calcium channel blockers (verapamil). Both drugs have negative chronotropic and inotropic effects on the heart, which can lead to additive cardiovascular suppression when combined.

**Why the Correct Answer is Right**
Metoprolol (a beta-1 selective blocker) reduces heart rate by blocking beta-adrenergic stimulation. Verapamil (a non-dihydropyridine CCB) inhibits calcium influx in the AV node, slowing conduction and reducing heart rate. Together, they synergistically decrease cardiac output and may cause **additive bradycardia** or AV block. This combination is contraindicated in patients with heart block due to the risk of severe cardiac depression.

**Why Each Wrong Option is Incorrect**
**Option A:** *Increased heart rate* is incorrect. Both drugs independently lower heart rate; their combination would not increase it.
**Option B:** *Increased cardiac output* is incorrect. Cardiac output depends on heart rate and stroke volume—both are reduced by these drugs.
**Option C:** *No effect on heart rate* is incorrect. The drugs act on overlapping pathways (beta-1 and calcium channels) to slow AV nodal conduction.

**Clinical Pearl / High-Yield Fact**
Never

✓ Correct Answer: B. Bradycardia with AV block