If heart rate increases while stroke volume stays constant, what happens to cardiac output?

If heart rate increases while stroke volume stays constant, what happens to cardiac output?

• A. Fluctuate
• B. Decrease
• C. Increase
• D. Stay the same

Answer: (C)

Cardiac output is determined by multiplying heart rate by stroke volume. If the heart rate rises while stroke volume stays the same, the product increases, so cardiac output increases. For example, with a stroke volume around 0.07 L per beat, a heart rate of 70 bpm gives about 4.9 L/min; raising the rate to 100 bpm with the same stroke volume yields about 7.0 L/min. This often happens during activity when sympathetic drive speeds up the heart but doesn’t immediately change the amount of blood pumped per beat. If filling time became so short that stroke volume dropped, the overall effect on cardiac output might differ, but with SV held constant, increasing heart rate raises output.

Cardiac output is determined by multiplying heart rate by stroke volume. If the heart rate rises while stroke volume stays the same, the product increases, so cardiac output increases. For example, with a stroke volume around 0.07 L per beat, a heart rate of 70 bpm gives about 4.9 L/min; raising the rate to 100 bpm with the same stroke volume yields about 7.0 L/min. This often happens during activity when sympathetic drive speeds up the heart but doesn’t immediately change the amount of blood pumped per beat. If filling time became so short that stroke volume dropped, the overall effect on cardiac output might differ, but with SV held constant, increasing heart rate raises output.