# What is the cardiac output?

Works out cardiac output from heart rate and stroke volume, or by the Fick principle from oxygen use and blood oxygen levels, with the cardiac index over the body surface area.

- Page: https://www.acalculator.org/health/cardiac-output-calculator
- JSON spec: https://www.acalculator.org/health/cardiac-output-calculator.json
- Version: 7cf9ad114f01

## Default answer

Example with the default inputs (Method HR × SV, Heart rate (beats/min) 70, Stroke volume (mL) 70, Height 5 ft 10 in, Weight 170 lb): The cardiac output is 4.9 L/min, a cardiac index of 2.51 L/min/m².

## Inputs

| Key | Label | Description |
| --- | --- | --- |
| method | Method | Heart rate × stroke volume, or the Fick principle from oxygen use and oxygen content. |
| hr | Heart rate (beats/min) | Heart rate in beats a minute, 20 to 250. |
| sv | Stroke volume (mL) | Blood pumped in one beat, in mL, 5 to 250. |
| vo2 | Oxygen use, VO2 (mL/min) | Oxygen consumption in mL a minute, measured or estimated, 50 to 2,000. |
| hb | Hemoglobin (g/dL) | Hemoglobin in g/dL, 3 to 25. |
| sao2 | Arterial saturation, SaO2 | Arterial oxygen saturation, 50% to 100%. |
| svo2 | Mixed venous saturation, SvO2 | Mixed venous oxygen saturation (pulmonary artery blood), 10% to 100%. |
| pao2 | Arterial PO2 (mmHg) | Arterial oxygen pressure in mmHg, 20 to 700. |
| pvo2 | Mixed venous PO2 (mmHg) | Mixed venous oxygen pressure in mmHg, 10 to 100. |
| height | Height | Height, for the body surface area: 50 cm to 250 cm. |
| weight | Weight | Weight, for the body surface area: 2 kg to 300 kg. |

## Outputs

| Key | Label | Description |
| --- | --- | --- |
| co | Cardiac output (L/min) | Litres of blood the heart pumps a minute, to 2 decimals. |
| ci | Cardiac index (L/min/m²) | Cardiac output ÷ body surface area, to 2 decimals. |
| bsa | Body surface area (m²) | Mosteller: √(height cm × weight kg ÷ 3,600), to 2 decimals. |
| avDiff | Arterial-venous O2 difference (mL/dL) | Fick only: arterial minus mixed venous oxygen content, to 2 decimals. |

## Method

CO = HR × SV ÷ 1,000 (L/min). Fick: CO = VO2 ÷ ((CaO2 − CvO2) × 10), with O2 content = 1.34 × Hb × saturation + 0.003 × PO2 (mL/dL). CI = CO ÷ BSA, BSA = √(cm × kg ÷ 3,600) (Mosteller).

## Assumptions

- The Fick method needs a mixed venous sample from the pulmonary artery and a measured or estimated oxygen use.
- Hemoglobin carries 1.34 mL of oxygen per gram when fully saturated; plasma carries 0.003 mL/dL per mmHg.
- The page shows the arithmetic for measured values. It is not a measurement and not a diagnosis.

## Worked examples

1. method = hrsv, hr = 70, sv = 70, height = 1.778, weight = 77.110703 gives co = 4.9, bsa = 1.951515, ci = 2.510869. Source: Demir 2025 and Mosteller 1987: CO = HR × SV = 70 × 70 = 4,900 mL/min = 4.9 L/min.
2. method = hrsv, hr = 60, sv = 80, height = 1.8, weight = 80 gives co = 4.8, bsa = 2, ci = 2.4.
3. method = fick, vo2 = 250, hb = 15, sao2 = 98%, svo2 = 75%, pao2 = 95, pvo2 = 40, height = 1.8, weight = 80 gives co = 5.221387, avDiff = 4.788, bsa = 2, ci = 2.610693. Source: Fick with the Nebout 2012 oxygen content: CaO2 = 1.34 × 15 × 0.98 + 0.003 × 95 = 19.983.

## FAQ

### How is cardiac output calculated?

Cardiac output is the blood the heart pumps each minute: heart rate × stroke volume. At 70 beats a minute and 70 mL a beat, it is 4,900 mL, or 4.9 L a minute.

### What is the Fick method?

The Fick principle says the oxygen the body uses each minute equals the blood flow times the oxygen the blood gives up. So cardiac output = oxygen use (VO2) ÷ (arterial oxygen content − mixed venous oxygen content).

### How is oxygen content worked out?

Oxygen content (mL per dL of blood) = 1.34 × hemoglobin (g/dL) × saturation + 0.003 × PO2 (mmHg), as in Nebout 2012. Hemoglobin carries most of the oxygen; the second term is the small amount dissolved in plasma. Some sources use 1.39 and 0.0031 instead, which gives a slightly different result.

### What is the cardiac index?

Cardiac output divided by body surface area, so people of different sizes can be compared. The page uses the Mosteller body surface area, √(height in cm × weight in kg ÷ 3,600).

### Where does the VO2 come from?

Ideally it is measured from the breath. When it is estimated, the Fick result is only as good as the estimate, so the page asks for the value and does not assume one.

### Does the page measure cardiac output?

No. It does the arithmetic on values measured elsewhere, such as an echo stroke volume or blood gas results.

## Sources

- Demir ZA, Bingül ES, Dost B, et al. Foundations and advancements in hemodynamic monitoring: Part I, elements of hemodynamics. Turk J Anaesthesiol Reanim. 2025;53(3):87-97. https://doi.org/10.4274/tjar.2025.251925 (open at https://pmc.ncbi.nlm.nih.gov/articles/PMC12123657/, retrieved 2026-10-05). Cited for CO = HR × SV, the Fick equation, and the cardiac index; it uses 1.39 and 0.0031 for oxygen content, and this page uses the 1.34 and 0.003 of Nebout 2012.
- Nebout S, Pirracchio R, et al. Should we monitor ScVO2 in critically ill patients? Cardiol Res Pract. 2012;2012:370697 (oxygen content CaO2 = Hb × 1.34 × SaO2 + 0.003 × PaO2). https://doi.org/10.1155/2012/370697 (open at https://pmc.ncbi.nlm.nih.gov/articles/PMC3177360/, retrieved 2026-10-05)
- Mosteller RD. Simplified calculation of body-surface area. N Engl J Med. 1987;317(17):1098. https://doi.org/10.1056/NEJM198710223171717 (retrieved 2026-10-05)