Cardiac output is defined as which of the following?

• A. Heart rate multiplied by stroke volume
• B. Heart rate divided by stroke volume
• C. Stroke volume only
• D. Blood pressure multiplied by heart rate

Answer: (A)

Cardiac output is the volume of blood the heart pumps each minute. It’s found by multiplying heart rate (beats per minute) by stroke volume (milliliters per beat): CO = HR × SV. For example, with a heart rate of 75 beats per minute and a stroke volume of 70 mL per beat, the cardiac output is about 75 × 70 = 5250 mL per minute (roughly 5.25 L/min).

Dividing heart rate by stroke volume doesn’t represent blood flow per minute; it would give a nonsensical unit for this context. Stroke volume alone is only the amount ejected per beat, not per minute. Blood pressure multiplied by heart rate mixes a pressure measure with rate, producing a value that isn’t a volume per minute, so it doesn’t define cardiac output.