**Core Concept**
Bradycardia refers to a slower than normal heart rate, typically defined as a resting heart rate of less than 60 beats per minute. This physiological response is often mediated by the autonomic nervous system, specifically through parasympathetic stimulation of the sinoatrial (SA) node.

**Why the Correct Answer is Right**
The correct answer is atropine, a medication that acts as a competitive antagonist to the muscarinic acetylcholine receptors (mAChRs) in the parasympathetic nervous system. By blocking these receptors, atropine inhibits the parasympathetic stimulation of the SA node, leading to an increase in heart rate. This is because the parasympathetic nervous system, through the release of acetylcholine, normally slows the heart rate. Atropine's blockade of mAChRs prevents this slowing, resulting in bradycardia.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is blank. Please fill in the blank.
**Option B:** This option is blank. Please fill in the blank.
**Option C:** This option is blank. Please fill in the blank.

**Clinical Pearl / High-Yield Fact**
Atropine is often used in clinical settings to treat bradycardia, as well as to dry up respiratory secretions and reduce salivation. However, it should be used cautiously in patients with glaucoma, as it can increase intraocular pressure.

**Correct Answer:** C. Atropine.