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
[{'content': 'Cardiac output varies under different physiological conditions. It is decreased by? \nSelect and explain. \nA. Increased hea rate, B. Decreased hea rate, C. Increased stroke volume, D. None of the above', 'role': 'user'}, {'content': 'Answer: B \nExplanation: 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.', 'role': 'assistant'}]