Cardiac Output (AQA A Level Biology): Revision Note

Step 1: find the heart rate

• Three cardiac cycles occur over the course of 3 seconds

  • There are two sets of valve sounds per cycle

  • We measure a full cardiac cycle by choosing any point within the cycle and then looking at the length of time that passes before we reach the same point in the next cycle

• One cardiac cycle = 1 second

• The number of cardiac cycles completed in a minute, or heart rate can be calculated as follows:

60 x 1 = 60 bpm

Step 2: insert relevant figures into the equation

cardiac output = heart rate x stroke volume

= 60 x 77

= 4620 cm³

Step 3: convert into the correct units

• 1 dm³ = 1000 cm³

4620 ÷ 1000 = 4.62 dm³

An individual has a cardiac output of 4.3 dm³ and a heart rate of 72 bpm.

Calculate the individual's stroke volume. Give your answer in cm³.

Step 1: rearrange the equation

Cardiac output = heart rate x stroke volume

Stroke volume = cardiac output ÷ heart rate

Step 2: insert relevant figures into the equation

4.3 ÷ 72 = 0.0597 dm³

Step 3: convert into the correct units

• 1 dm³ = 1000 cm³

0.0597 x 1000 = 59.7 cm³