Cardiac index (CI) is a haemodynamic parameter that relates the cardiac output (CO) from left ventricle in one minute to body surface area (BSA),^[1] thus relating heart performance to the size of the individual. The unit of measurement is litres per minute per square metre (L/min/m²).

The index is usually calculated using the following formula:^{[citation needed]}

${\displaystyle {\text{CI))={\frac {\text{CO)){\text{BSA))}={\frac ((\text{SV))\times {\text{HR))}{\text{BSA))))$

where

CI

Cardiac index

BSA

Body surface area

SV

Stroke volume

HR

Heart rate

CO

Cardiac output

The normal range of cardiac index at rest is 2.6–4.2 L/min/m².

The cardiac index is frequently measured and used in both intensive care medicine and cardiac intensive care. The CI is a useful marker of how well the heart is functioning as a pump by directly correlating the volume of blood pumped by the heart with an individual's body surface area.^{[citation needed]}

If the CI falls acutely below 2.2 L/min/m², the patient may be in cardiogenic shock.^{[citation needed]}