Cardiac Output - The Heart

Cardiac output can be discussed as the heart rate (HR) and stroke volume (SV) which is the amount of blood ejected with each beat of the heart

Cardiac Output = Heart Rate x Stroke Volume

Q = HR x SV

When resting an average person’s stroke volume is 70ml per beat and 70 beats per minute. This results in a cardiac output of approx 5,000ml per minute or 5 litres per minute. The cardiac output requirement is determined by the demand for oxygen at rest and the need to supply a high blood flow to the kidneys.

The cardiac output doesn’t change during rest as a result of aerobic training, however, the way in which the heart delivers the resting demand does. For example :

Following 6 to 8 months of aerobic training the resting heart rate could decrease to 50 beats per minute.

Resting stroke volume could increase to approximately 100ml per beat.

Depending on the intensity of exercise, cardiac output will increase rapidly and then gradually until a steady state is reached.

An average cardiac output for a resting healthy male is 5 litres per minute.

During exercise this may increase by as much as 25 to 30 litres per minute.

In endurance athletes this could raise to 35 to 40 litres per minute.