A big person needs more blood flow than a small one, so cardiac output is often indexed to body surface area. A cardiac index below about 2.2 L/min/m² with signs of poor perfusion suggests cardiogenic shock.
How to use the Cardiac Index Calculator
- Cardiac output
- Heart rate
- Height
- Weight
Results update as you type, and every field accepts the units shown in its menu.
How it works
Enter cardiac output (from echo, thermodilution or the cardiac output calculator), heart rate, height and weight.
Inputs explained
| Field | What to enter |
|---|---|
| Cardiac output | In L/min |
| Heart rate | In bpm |
| Height | Units: cm, in, m, ft, mm |
| Weight | Units: kg, lb, st, g |
What each result means
- Body surface area = sqrt([Height]×[Weight]÷3600)
- Cardiac index = [Cardiac output]÷[Body surface area]
- Stroke volume index = [Cardiac index]÷[Heart rate]×1000
Example values
How the main result changes when Cardiac output changes and everything else stays at the example values above:
| Cardiac output (L/min) | Cardiac index (L/min/m²) |
|---|---|
| 2.75 | 1.44 |
| 4.13 | 2.16 |
| 5.5 | 2.88 |
| 6.88 | 3.6 |
| 8.25 | 4.32 |
| 11 | 5.76 |
Health note: this calculator is for education and screening only and is not a diagnosis or treatment advice. Discuss your results with a qualified clinician.
Formula
BSA = √(height cm × weight kg ÷ 3600)
CI = CO ÷ BSA
SVI = CI ÷ HR × 1000
Worked example
Inputs — Cardiac output: 5.5 L/min; Heart rate: 75 bpm; Height: 175 cm; Weight: 75 kg.
Results — Body surface area = 1.91 m²; Cardiac index = 2.88 L/min/m²; Stroke volume index = 38 mL/m².
Key terms
- CI
- Cardiac index.
- SVI
- Stroke volume index.
Frequently asked questions
What is a normal cardiac index?
About 2.5–4.0 L/min/m².
What does a low cardiac index mean?
The heart is not pumping enough blood for the body's size; it is a feature of cardiogenic shock.
What is a normal stroke volume index?
About 33–47 mL/m².