Heart & Lungs

How much blood does the heart pump, and how much oxygen does it bring to the body? From the heart rate, the volume of the left ventricle and the blood pressure, get the cardiac output, ejection fraction, mean arterial pressure and vascular resistance. Add the haemoglobin and oxygen saturation for the oxygen delivery and, with a venous saturation, the oxygen the body uses (Fick).

PhysiologyCardiovascularOxygen transport

Inputs

Input examples

EDV and ESV are the volumes of the left ventricle at the end of filling (diastole) and at the end of pumping (systole), as measured by ultrasound; their difference is the stroke volume. If you only know the stroke volume, choose Stroke volume. Fields marked optional can be left empty: the central venous pressure gives the vascular resistance, height and weight give the values per m² of body surface, and the venous saturation (SvO₂, mixed venous blood) gives the oxygen use. Haemoglobin in g/dL, g/L or mmol/L (used in the Netherlands); oxygen pressure in mmHg or kPa. For education only — not medical advice.

Heart rate HR — beats per minute

Stroke volume from

End-diastolic volume EDV — mL

End-systolic volume ESV — mL

Systolic pressure SBP — mmHg

Diastolic pressure DBP — mmHg

Central venous pressure CVP — mmHg, optional

Height — cm, optional

Weight — kg, optional

Also calculate the oxygen delivery?

Haemoglobin Hb

Arterial PaO₂

Arterial saturation SaO₂ — %

Venous saturation SvO₂ — %, optional

How Does the Heart Deliver Oxygen?

With every beat the left ventricle fills to its end-diastolic volume and then squeezes out part of it, the stroke volume. The share it squeezes out is the ejection fraction, the number cardiologists use most to judge how well the heart pumps. Stroke volume times heart rate is the cardiac output: about 5 litres per minute at rest, so all your blood goes round once a minute, and up to 20–35 L/min in a trained athlete during exercise.

The pressure in the arteries swings between the systolic and diastolic value. Because the heart spends about two thirds of each beat relaxing, the mean arterial pressure lies one third of the way up from the diastolic pressure. Like Ohm’s law for electricity, pressure drop = flow × resistance, so the pressure drop from arteries to veins divided by the cardiac output is the systemic vascular resistance, set mainly by how wide the small arteries are.

Each gram of haemoglobin carries up to 1.34 mL of oxygen; only a little dissolves in the plasma. The oxygen content of the blood times the cardiac output is the oxygen delivery. At rest the body takes out only about a quarter of it, so the blood that returns to the heart is still about 75% saturated: a reserve for exercise or illness. The Fick principle turns this around: the oxygen used equals the flow times the difference between arterial and venous content.

at restCO ≈ 5 L/min, EF 50–70%

EF ≤ 40%heart failure with reduced EF

MAP < 65 mmHgorgans may get too little blood

1 g Hbbinds 1.34 mL O₂

Pressure–Volume Loop of the Left Ventricle

one heartbeat, anticlockwise (simplified)

area ≈ work done per beat

Result

Enter the values above

For education only, not medical advice. These are simplified estimates compared with average adult values. Do not use them to diagnose or treat anyone; ask a doctor about real measurements.

Compared With a Healthy Adult at Rest

typical ranges; labs and guidelines differ slightly

Quantity	Your values	Typical at rest

Worked Techniques

Stroke Volume and Output

Subtract the volume left after a beat from the volume before it, then multiply by the beats per minute. Divide by 1000 to go from mL to litres.

Example: 72 beats/min × 70 mL = 5.04 L/min, the textbook resting value.

Mean Pressure and Resistance

The factor 80 converts mmHg·min/L (Wood units) to dyn·s/cm⁵, the unit used in intensive care.

Example: the same drop with half the output means twice the resistance: the vessels have narrowed.

Oxygen Content, Delivery and Use

Multiply by 10 because the content is per decilitre and the output in litres. The venous content uses the venous saturation and a PvO₂ of 40 mmHg for the small dissolved part.

Example: 4.9 L/min × 20.0 mL/dL × 10 = 980 mL O₂ per minute delivered, of which 235 mL (24%) is used.

Sources & Verification

References

J. E. Hall and M. E. Hall, Guyton and Hall Textbook of Medical Physiology, 14th ed., Elsevier, 2021 — the chapters on the heart as a pump, cardiac output and the transport of oxygen in the blood.
P. L. Marino, Marino’s The ICU Book, 4th ed., Wolters Kluwer, 2014 — oxygen content, delivery, uptake and extraction; haemodynamic normal values.
R. D. Mosteller, “Simplified calculation of body-surface area”, N. Engl. J. Med. 317 (1987) 1098 — BSA = √(height × weight / 3600).
B. Bozkurt et al., “Universal definition and classification of heart failure”, J. Card. Fail. 27 (2021) 387–413 — EF ≤ 40% reduced, 41–49% mildly reduced, ≥ 50% preserved.