During exercise, which of the following occurs?

• A. Heart rate increases
• B. Stroke volume decreases
• C. Cardiac output decreases
• D. Venous return decreases

Answer: (A)

During exercise, the body needs more oxygen and nutrients to working muscles, so the heart responds by increasing how often it beats. This rise in heart rate is a major reason why cardiac output goes up, since cardiac output is the product of heart rate and stroke volume. Stroke volume does not typically drop during exercise; it often increases early on as venous return improves and the heart contracts more forcefully, with contractility enhanced by sympathetic stimulation. Venous return itself actually increases during activity because contracting muscles squeeze the veins (the muscle pump) and breathing movements help move blood back to the heart. So the most consistent change during exercise is an increase in heart rate, which drives cardiac output higher, rather than decreases in stroke volume, venous return, or overall cardiac output.