What is the difference between cardiac output and cardiac index?

Cardiac output (CO) is the total volume of blood pumped by the heart per minute (L/min). Cardiac index (CI) normalizes CO to body surface area (L/min/m²), allowing comparison across patients of different sizes. CI is the preferred clinical parameter.

How is stroke volume measured?

Stroke volume can be measured by echocardiography (LVOT VTI method), pulmonary artery catheter (thermodilution), arterial waveform analysis (FloTrac, PiCCO), or estimated from biometric data. Echo-derived SV is the most common non-invasive method.

What causes low cardiac index?

Low CI can result from reduced contractility (heart failure, MI), inadequate preload (hypovolemia, tamponade), excessive afterload (aortic stenosis, hypertension), or arrhythmias. The treatment depends on the underlying cause.

What does a high cardiac index mean?

CI >4.0 can be physiologic (exercise, pregnancy) or pathologic (sepsis, anemia, thyrotoxicosis, AV fistula, liver cirrhosis). High-output states often have low SVR and may still cause organ hypoperfusion in distributive shock.

Why is BSA used instead of body weight?

BSA better reflects metabolic rate and oxygen consumption than weight alone. Since cardiac output exists to meet metabolic demands, normalizing to BSA provides a more physiologically meaningful index of cardiac performance adequacy.

Is the Du Bois formula accurate for all patients?

The Du Bois formula may be less accurate in obese patients, children, or those with extremes of body habitus. Alternative formulas (Mosteller, Haycock) exist for specific populations. For clinical CI calculations, the differences are generally small.

Cardiac Index Calculator

Calculate cardiac index, cardiac output, and stroke volume index from heart rate, stroke volume, and body surface area. Classifies hemodynamic status.

⚠️ Medical Disclaimer: This calculator provides estimates for educational purposes. True cardiac output measurement requires invasive monitoring (PA catheter, PiCCO) or echocardiographic techniques.

Sex

Height

Weight

Heart Rate

bpm

Stroke Volume

Cardiac Index2.64 L/min/m²

▼

ShockLowNormal (2.2-4.0)ElevatedVery High

Cardiac Index Classification

2.64

Normal

Normal cardiac index range

Cardiac Output (CO)

5.04 L/min

HR × SV / 1000 — total flow per minute

Cardiac Index (CI)

2.64 L/min/m²

CO normalized to BSA — Normal

Stroke Volume Index (SI)

36.7 mL/m²

Normal (33-47)

Body Surface Area

1.91 m²

Mosteller formula

Est. SVR

1,143 dyn·s/cm⁵

Normal (800-1200)

BMI

24.5

Male, 175 cm, 75 kg

Parameter	Normal Range	Your Value	Status
Cardiac Output	4-8 L/min	5.04 L/min	✓ Normal
Cardiac Index	2.2-4.0 L/min/m²	2.64 L/min/m²	✓ Normal
Stroke Volume	60-100 mL	70 mL	✓ Normal
SV Index	33-47 mL/m²	36.7 mL/m²	✓ Normal
Heart Rate	60-100 bpm	72 bpm	✓ Normal
BSA	1.5-2.2 m²	1.91 m²	✓ Normal

CI Range	Classification	Common Causes
<1.8	Cardiogenic Shock	Acute MI, severe CHF, tamponade, massive PE
1.8-2.2	Low Output	Heart failure, hypovolemia, post-cardiac surgery
2.2-4.0	Normal	Healthy resting cardiac function
4.0-5.0	Elevated	Exercise, anxiety, pregnancy, mild sepsis
>5.0	Hyperdynamic	Sepsis, anemia, thyrotoxicosis, AV fistula

Planning notes, formulas, and examples

About the Cardiac Index Calculator

The Cardiac Index Calculator computes cardiac output (CO), cardiac index (CI), and stroke volume index (SI) from heart rate, stroke volume, and body surface area. Normalizing output to body size makes the numbers easier to compare across patients.

Cardiac index is commonly used in critical care, cardiology, and perioperative medicine. Typical CI values are about 2.2 to 4.0 L/min/m², with values below 1.8 suggesting low output and very high values pointing toward a hyperdynamic state.

The calculator also reports systemic vascular resistance when MAP and CVP are available, so you can see whether a low CI is more consistent with poor pump function, low preload, or reduced vascular tone.

When This Page Helps

Cardiac output alone can be misleading because it does not account for body size. A value that is acceptable for one patient may be inadequate for another.

CI helps clinicians compare perfusion targets, assess shock states, and follow hemodynamic trends after fluids, vasopressors, or inotropes.

How to Use the Inputs

Select the patient sex.
Enter height and weight for BSA calculation.
Enter the current heart rate in beats per minute.
Enter the measured or estimated stroke volume in mL.
Review cardiac output, cardiac index, and hemodynamic classification.
Compare the result with the reference range shown on the page.
Use the trend, not a single number, when following treatment response.

Formula used

CO = HR × SV / 1000 (L/min)
BSA = √(Height × Weight / 3600) [Mosteller]
CI = CO / BSA (L/min/m²)
SI = SV / BSA (mL/m²)
SVR = 80 × (MAP - CVP) / CO (dyn·s/cm⁵)

Example Calculation

Result: CI 2.61 L/min/m² — Normal

CO = 72 × 70 / 1000 = 5.04 L/min. BSA = √(175 × 75 / 3600) = 1.93 m². CI = 5.04 / 1.93 = 2.61 L/min/m², which is within the normal range (2.2-4.0).

Tips & Best Practices

Echo-derived stroke volume is the most common non-invasive input.
Low CI with high SVR usually points toward a cardiogenic pattern.
High CI with low SVR is more consistent with distributive shock.
Follow the trend over time when reassessing treatment response.
In patients at body-size extremes, the BSA estimate matters as much as the raw output.
Athletes can have a much higher CI than sedentary adults at rest.

Hemodynamic Profiling in Critical Care

The cardiac index is one part of hemodynamic assessment. It is often interpreted alongside preload, afterload, and contractility to help explain why perfusion is low or high.

Fluid Responsiveness

When the cardiac index improves after a fluid challenge, it can suggest that the patient is preload responsive. That makes serial measurements more useful than a single snapshot.

Interpreting the Result

A low CI can reflect poor pump function, low circulating volume, or excessive afterload. A high CI can appear in pregnancy, exercise, sepsis, anemia, or other high-output states.

Sources & Methodology

Last updated: March 26, 2026

Methodology

This calculator defines cardiac index in the standard way as cardiac output divided by body surface area, with optional derived values such as stroke-volume index and an estimated SVR layer for context. The page is most useful as a quick normalization tool when the user already has a stroke-volume estimate from echocardiography or another hemodynamic method.

The output should not be treated as a universal invasive hemodynamic measurement. Reference ranges vary with how cardiac output and stroke volume were obtained, and any SVR estimate built from assumed MAP or CVP values is only a rough orientation aid rather than a formal bedside hemodynamic diagnosis.

Sources

Simplified calculation of body-surface area (PubMed / New England Journal of Medicine) — Mosteller BSA equation used by the page.
Normal Values of Cardiac Output and Stroke Volume According to Measurement Technique, Age, Sex, and Ethnicity: Results of the World Alliance of Societies of Echocardiography Study (PubMed / Journal of the American Society of Echocardiography)
Cardiac index (NCBI MedGen)

Frequently Asked Questions

Cardiac output (CO) is the total volume of blood pumped by the heart per minute (L/min). Cardiac index (CI) normalizes CO to body surface area (L/min/m²), allowing comparison across patients of different sizes. CI is the preferred clinical parameter.