Why does nicotine cause tachycardia when it stimulates the parasympathetic nervous system?

Nicotine primarily stimulates the sympathetic nervous system rather than the parasympathetic nervous system. When nicotine binds to nicotinic acetylcholine receptors, it leads to the release of neurotransmitters like norepinephrine, which increases heart rate and causes tachycardia. Additionally, while the parasympathetic system generally slows the heart rate, nicotine's overall stimulatory effects on the body dominate, resulting in an increased heart rate.