What effect does atropine have on the heart?

Atropine is an anticholinergic medication that primarily works by blocking the action of acetylcholine on muscarinic receptors in the heart and other tissues. Specifically, in the context of heart function, atropine inhibits the parasympathetic influence exerted by the vagus nerve. The vagus nerve typically acts to decrease heart rate by releasing acetylcholine, which, through muscarinic receptors, slows down the heart rate and reduces conduction velocity through the atrioventricular (AV) node.

When atropine is administered, it competes with acetylcholine and effectively reduces the parasympathetic tone on the heart. As a result, the heart rate increases due to the unopposed influence of the sympathetic nervous system. This increase in heart rate can be beneficial in situations of bradycardia (abnormally slow heart rate), as atropine can help restore a more normal heart rhythm.

In summary, atropine's mechanism of action leads to a significant increase in heart rate by blocking parasympathetic activity mediated by acetylcholine, making the correct answer directly reflect this pharmacological effect.