How is cardiac output calculated, and what is the normal resting range for adults?

• A. Cardiac output = stroke volume × heart rate; normal resting range is 4–6 L/min
• B. Cardiac output = stroke volume × heart rate; normal resting range is 6–8 L/min
• C. Cardiac output = stroke volume + heart rate; normal resting range is 4–6 L/min
• D. Cardiac output = stroke volume ÷ heart rate; normal resting range is 4–6 L/min

Answer: (A)

Cardiac output is the volume of blood the heart pumps per minute. It’s calculated by multiplying the amount of blood ejected with each beat (stroke volume) by how many beats occur each minute (heart rate). Since stroke volume is measured in milliliters per beat and heart rate in beats per minute, their product gives CO in milliliters per minute, which is typically expressed in liters per minute when summed across the heart’s activity.

If the stroke volume is about 70 mL per beat and heart rate is about 70 beats per minute, you get roughly 4.9 L/min, a number that sits in the normal resting range for adults. In healthy adults at rest, a typical range is approximately 4–6 L/min, with variation based on body size and fitness.

The other approaches aren’t correct because cardiac output isn’t obtained by adding or dividing stroke volume and heart rate; those operations don’t yield a flow rate per minute.