This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Heart, Circulation, and Blood, Subject name: Physiology
Cardiac output increase in exercise by 
Select and explain. 
A. Increase in heart rate, B. Increase in preload, C. Increase in afterload, D. Sympathetic stimulation
A: Increase in heart rate
Answer: A: Increase in heart rate 
Explanation: Ans: a (Increase in HR) Ref: Ganong 22nd ed/ p.632, 633In muscular exercise there is increase in sympathetic activity resulting in increased cardiac contractility and heart rate. Rise in heart rate is the major event that occur in normal individuals compared to increase in contractility, remember Cardiac output = HR X Stroke volumeTherefore, cardiac output increases in normal individuals at the cost of increase in heart rate.