This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pharmacology
Intravenous administration of norepinephrine in a patient already taking an effective dose of atropine will often: 
Select and explain. 
A. Increase heart rate, B. Decrease total peripheral resistance, C. Decrease pupil size, D. Has no effect on cardiovascular system
A: Increase heart rate
Answer: A: Increase heart rate 
Explanation: None