Calculating how much blood is pumped by the heart

Cardiac output

Cardiac output is the total volume of blood pumped out by the left ventricle every minute. It can be calculated using the following equation:

\text{cardiac output} = \text{stroke volume} \times \text{heart rate}

\text{CO} = \text{SV} \times \text{HR}

Units:

  • CO - cm3 per minute (cm3/min)
  • SV - cm3
  • HR - beats per minute (bpm) (beats/min)

Stroke volume is the volume of blood pumped out of the left ventricle each time the heart beats

Heart rate is the number of beats per minute and is the same as your pulse rate.

If the heart rate increases, cardiac output increases. Also if stroke volume increases, cardiac output will increase.

Calculating SV or HR

Either rearrange the above equation (SV = CO/HR or HR = CO/SV)

Or use this formula triangle to help:

Formula triangle of cardiac output, stroke volume and heart rate

Cover up what you want to find with your finger and write down what is left. This will give the correct formula. If you want SV, cover SV with your finger and you are left with CO/HR.

For example, if the stroke volume at rest is 70 cm3 and the heart rate is 70 bpm, then the cardiac output is 70 × 70 cm3 per minute = 4900 cm3 per minute.

Question

If the SV is 72 cm3 and the CO is 5400 cm3/min, what is the HR?

HR = CO/SV = 5400/72 = 75 bpm

During exercise, the heart rate increases and the force of contraction of the ventricles increases, therefore cardiac output and stroke volume increase.