Cardiac output calculator with stroke volume and ejection fraction

Cardiac output is the volume of blood one ventricle pumps each minute: cardiac output = heart rate × stroke volume. A heart beating 72 times a minute and pumping 70 cm³ (70 mL) each beat has a cardiac output of 72 × 70 = 5,040 cm³ per minute, or 5.04 litres per minute. This cardiac output calculator works it out, rearranges for heart rate or stroke volume, and finds stroke volume and ejection fraction from the volumes in the ventricle.

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Cardiac Output Calculator

Link heart rate, stroke volume and cardiac output

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How to use the cardiac output calculator

1. Open the Cardiac Output Calculator and choose what to find under Calculate: Cardiac output, Stroke volume, Heart rate or Ejection fraction.
2. Type the two values you know. Heart rate is in beats per minute (bpm), stroke volume in cm³ and cardiac output in dm³ per minute. 1 cm³ is 1 mL and 1 dm³ is 1 litre, so mL and L/min go straight in.
3. For ejection fraction, type the end-diastolic volume and end-systolic volume in cm³. Add the heart rate too if you want the cardiac output as well.
4. Read the answer with its working. Under it you get the output in cm³ per minute and how long one heartbeat lasts, or for ejection fraction, the stroke volume and where the value sits against the usual adult resting bands.
5. The graph shows cardiac output against heart rate at your stroke volume, with your heart rate marked. For practice questions with worked answers, press Random problem.

The cardiac output formula

Rearranged, SV = CO ÷ HR and HR = CO ÷ SV. The units are what trip people up: HR × SV in cm³ gives cm³ per minute, so divide by 1,000 for dm³ (litres) per minute. When you rearrange, turn the cardiac output back into cm³ first by multiplying by 1,000.

Stroke volume and ejection fraction

The ventricle is fullest at the end of diastole, when it has filled, and emptiest at the end of systole, when it has contracted. The difference is what left in that beat:

Normal cardiac output and typical values

These are the figures OpenStax Anatomy and Physiology gives for a resting 70 kg adult, and they apply to each ventricle separately. In hard exercise a healthy young person's heart rate can reach about 150 bpm and stroke volume about 130 mL, pushing cardiac output to around 19.5 L/min, four to five times the resting value.

Here x is the heart rate in beats per minute and y is the cardiac output in litres per minute, with the stroke volume held at 70 mL. Doubling the heart rate doubles the output. In real exercise the stroke volume rises too, so the output climbs faster than this line.

Worked examples you can check in the calculator

Example 1: cardiac output at rest

Heart rate 72 bpm, stroke volume 70 cm³. Choose Cardiac output and type both.

The calculator also shows that one heartbeat lasts 60 ÷ 72 = 0.833 s.

Example 2: during exercise

A cyclist's heart rate rises to 160 bpm and their stroke volume to 125 cm³. CO = 160 × 125 = 20,000 cm³ per minute = 20.0 dm³ per minute, about four times the resting value in Example 1. Each beat now lasts only 0.375 s.

Example 3: finding stroke volume

Cardiac output is 6.3 dm³ per minute at 84 bpm. Choose Stroke volume. First turn the output into cm³: 6.3 × 1,000 = 6,300 cm³ per minute. Then SV = 6,300 ÷ 84 = 75 cm³.

Example 4: an athlete's resting heart rate

Training makes the heart muscle stronger, so it pumps more per beat. A trained runner at rest has a cardiac output of 5.0 dm³ per minute and a stroke volume of 100 cm³. Choose Heart rate: HR = 5,000 ÷ 100 = 50 bpm. The same output as an untrained person, from fewer beats.

Example 5: ejection fraction

A left ventricle holds 130 cm³ when full and 55 cm³ after contracting, at a heart rate of 68 bpm. Choose Ejection fraction and type all three.

The calculator places 57.7% in its typical band, 50 to 70%, and with the heart rate gives CO = 68 × 75 = 5,100 cm³ per minute, or 5.1 dm³ per minute. If the same heart filled to 180 cm³ but only emptied to 120 cm³, the ejection fraction would be 60 ÷ 180 × 100 = 33.3%, which falls in its reduced band, below 40%.

Try a cardiac output question, then press Mark to check your answer in the Human Physiology course.

What changes cardiac output

• Heart rate is set by the sinoatrial node and changed by nerves and hormones. Sympathetic nerves and adrenaline raise it; the parasympathetic vagus nerve lowers it.
• Preload, another way of saying end-diastolic volume. A ventricle that fills more is stretched more and contracts harder, so stroke volume rises.
• Contractility, the force of each contraction. Sympathetic stimulation increases it.
• Afterload, the pressure the ventricle must push against. Higher afterload, from narrowed arteries or a stiff valve, lowers stroke volume.

What the calculator doesn't do

It works with heart rate, stroke volume and ventricle volumes, the way biology courses teach cardiac output. It doesn't do clinical measures such as cardiac index or the Fick method, and it isn't a medical tool: its bands are a guide for study, not a diagnosis. It also won't take a heart rate from a pulse count. Count beats for 15 seconds and multiply by 4 first: 18 beats in 15 seconds is 72 bpm.

Common mistakes

• Forgetting to convert units. 72 × 70 is 5,040 cm³ per minute, not 5,040 litres. Divide by 1,000 for dm³.
• Dividing by the wrong thing. To find stroke volume, divide the output by the heart rate, after turning the output into cm³.
• Using EDV as the stroke volume. Stroke volume is EDV − ESV, what leaves in a beat, not what the ventricle holds.
• Dividing EF by ESV. Ejection fraction is SV ÷ EDV, the share of the full ventricle that is pumped out.
• Doubling for both ventricles. Cardiac output is for one ventricle. The left and right pump about the same volume.

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