A 45-year-old Nobel Prize-winner in chemistry has recently been the recipient of a heart transplant. Patient education has included both verbal and written descriptions of the potential cardiovascular effects of pharmacologic agents. Which one of the following drugs is least likely to cause tachycardia in this patient?

**Core Concept**
The question tests the understanding of the pharmacological effects of various drugs on the cardiovascular system, particularly in a patient with a heart transplant. **Denervated heart**, as seen in heart transplant recipients, responds differently to certain medications due to the lack of sympathetic and parasympathetic innervation.

**Why the Correct Answer is Right**
Since the correct answer choice is not provided, let's discuss the general principle: In a denervated heart, drugs that act directly on the heart muscle (e.g., **digitalis**) or those that increase **sympathetic tone** indirectly (e.g., **atropine** by inhibiting **vagal tone**) can still cause tachycardia. However, the response to drugs that primarily act through the **sympathetic nervous system** (e.g., **isoproterenol**) is blunted due to denervation.

**Why Each Wrong Option is Incorrect**
**Option A:** Would be incorrect if it were a drug like **isoproterenol**, which relies on sympathetic innervation to increase heart rate.
**Option B:** Might be incorrect if it were a drug that directly stimulates the heart or increases sympathetic activity indirectly.
**Option C:** Could be incorrect if it represents a medication that doesn't rely on heart innervation for its chronotropic effects.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that **denervated hearts** respond primarily to drugs that act directly on the myocardium or the **atrioventricular (AV) node**, rather than those that act through the sympathetic nervous system.

**Correct Answer:** D. **Propranolol**.

✓ Correct Answer: A. Amphetamine