Calculating how much blood is pumped by the heart

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)

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

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?

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

Cellular respiration and transport - Edexcel Calculating how much blood is pumped by the heart