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: Physiology
Cardiac output varies under different physiological conditions. It is decreased by? 
Select and explain. 
A. Increased hea rate, B. Decreased hea rate, C. Increased stroke volume, D. None of the above
B: Decreased hea rate
Answer: B: Decreased hea rate 
Explanation: Cardiac output is the product of the hea rate and stroke volume (CO = HR x SV). Therefore, cardiac output decreases by bradycardia. Ref: Mohrman D.E., Heller L.J. (2010). Chapter 3. The Hea Pump. In D.E. Mohrman, L.J. Heller (Eds), Cardiovascular Physiology, 7e.