Which medication is primarily used to increase heart rate?

Atropine is primarily used to increase heart rate, particularly in situations where bradycardia (slow heart rate) is present. This medication acts as an anticholinergic agent, meaning it blocks the effects of the vagus nerve on the heart. By inhibiting the action of acetylcholine on the parasympathetic nervous system, Atropine leads to an increase in heart rate by reducing the inhibitory influences on the sinoatrial (SA) node, which is responsible for initiating the heartbeat.

In clinical practice, Atropine is often administered in acute scenarios such as symptomatic bradycardia, where immediate action is required to restore adequate heart function. This mechanism of action is distinct and specifically targeted for increasing heart rate, making Atropine the appropriate choice among the options provided.