Final answer:
Atropine, an anticholinergic medication, blocks the parasympathetic system's effects on the heart, which normally slows the heart rate. This blockage increases the heart rate by suppressing parasympathetic stimulation, potentially up to the intrinsic heart rate of approximately 100 bpm.
Step-by-step explanation:
At normal doses, atropine has a specific effect on the heart rate. Atropine is an anticholinergic drug, which means it blocks the activity of the neurotransmitter acetylcholine at muscarinic receptors. Since acetylcholine is associated with parasympathetic stimulation, the presence of atropine suppresses this parasympathetic influence on the heart. One of the primary roles of the parasympathetic system, especially the vagus nerve, is to decrease heart rate and stroke volume. Thus, by inhibiting this effect, atropine allows the heart rate to increase.
Without parasympathetic input, the heart would naturally work at a rate of about 100 beats per minute (bpm). Therefore, administration of atropine could lead to an increase in heart rate up to these levels. However, it's noteworthy that any increases beyond this rate would require additional sympathetic stimulation. Atropine is often used medically to increase the heart rate in cases where bradycardia (a slower-than-normal heart rate) is present and needs to be corrected.