If stroke volume decreases while heart rate remains constant, what happens to cardiac output?

If stroke volume decreases while heart rate remains constant, what happens to cardiac output?

• A. CO increases.
• B. CO stays the same.
• C. CO decreases.
• D. CO becomes zero.

Answer: (C)

Cardiac output is the product of heart rate and stroke volume. If stroke volume decreases while heart rate stays the same, the overall output must fall because you’re multiplying a smaller stroke volume by the unchanged rate. For example, with a heart rate of 70 beats per minute, if stroke volume drops from 70 mL to 60 mL per beat, cardiac output goes from about 4900 mL/min to 4200 mL/min. Stroke volume can decrease due to factors like reduced venous return (lower preload), increased afterload, or weaker contractility, and with no change in heart rate there isn’t a compensatory increase to keep the output up. The other options would require the heart to beat faster, to eject more blood per beat, or to stop pumping entirely, none of which is given here.

Cardiac output is the product of heart rate and stroke volume. If stroke volume decreases while heart rate stays the same, the overall output must fall because you’re multiplying a smaller stroke volume by the unchanged rate. For example, with a heart rate of 70 beats per minute, if stroke volume drops from 70 mL to 60 mL per beat, cardiac output goes from about 4900 mL/min to 4200 mL/min. Stroke volume can decrease due to factors like reduced venous return (lower preload), increased afterload, or weaker contractility, and with no change in heart rate there isn’t a compensatory increase to keep the output up. The other options would require the heart to beat faster, to eject more blood per beat, or to stop pumping entirely, none of which is given here.