Cardiac output is calculated as which of the following?

• A. Heart rate times blood pressure
• B. Stroke volume divided by heart rate
• C. Cardiac output divided by systemic vascular resistance
• D. Heart rate times stroke volume

Answer: (D)

The key idea is that cardiac output is the volume of blood the heart pumps per minute, determined by how often it beats and how much blood is pumped with each beat. Multiply heart rate (beats per minute) by stroke volume (mL per beat) to get cardiac output (mL per minute). For example, 70 beats per minute with a stroke volume of about 70 mL per beat yields roughly 4900 mL per minute (about 5 L/min).

Using blood pressure with heart rate would mix a pressure with a flow quantity and doesn’t give volume per time. Dividing stroke volume by heart rate would produce an odd unit and doesn’t reflect the actual flow. Dividing cardiac output by systemic vascular resistance ties into a different relationship (MAP ≈ CO × SVR, so CO ≈ MAP / SVR), not the direct calculation of cardiac output. The straightforward, widely used formula is heart rate times stroke volume.