Heart Score Calculator
3 methods · Formula review July 2026

Cardiac Output Calculator

Calculate how much blood the heart pumps per minute using heart rate and stroke volume, the direct Fick principle, or Doppler echocardiography with LVOT diameter and VTI. Add height and weight to calculate body surface area and cardiac index.

Basic formula: Cardiac output (L/min) = heart rate (beats/min) × stroke volume (mL/beat) ÷ 1,000.
3
Methods
CO
L/min
CI
Optional Index

For adult education and clinician calculation support. Cardiac output depends on method, loading conditions, rhythm, measurement quality, and clinical context. Do not diagnose shock or guide treatment from this page alone.

Hemodynamic calculation

Choose a Method

Calculated locally

Use when heart rate and stroke volume are already known.

＋ Add height and weight for cardiac index

Both fields are required for Mosteller body surface area and cardiac index.

How to Calculate Cardiac Output

Cardiac output (CO) is the volume of blood pumped by a ventricle each minute. The simplest relationship multiplies the number of beats per minute by the volume ejected with each beat.

Cardiac Output Calculator Infographic
CO = HR × SV ÷ 1,000

For example, a heart rate of 72 beats/min and stroke volume of 70 mL/beat produce 5,040 mL/min, or 5.04 L/min. The equation is exact arithmetic, but the accuracy of the result depends on how heart rate and stroke volume were measured.

Three Cardiac Output Calculation Methods

1

Heart rate × stroke volume

Best when HR and SV are already known. It exposes the fundamental physiological relationship without estimating either input.

2

Direct Fick principle

Uses measured oxygen consumption and arterial–mixed venous oxygen content difference.

3

Echo LVOT/VTI

Estimates stroke volume from Doppler flow distance and LVOT cross-sectional area.

Fick Cardiac Output Calculator Formula

The Fick principle states that whole-body oxygen consumption equals blood flow multiplied by the arterial–venous oxygen content difference. Rearranging the relationship gives:

CO = VO₂ ÷ (CaO₂ − CvO₂) ÷ 10

The final division by 10 applies when VO₂ is entered in mL/min and oxygen content is in mL O₂/dL, converting dL/min to L/min. For VO₂ 250 mL/min, CaO₂ 20 mL/dL, and CvO₂ 15 mL/dL, cardiac output is 250 ÷ 5 ÷ 10 = 5.0 L/min.

Direct versus assumed Fick: direct Fick measures oxygen consumption. Assumed Fick substitutes an estimated VO₂ equation and can introduce clinically meaningful error. This calculator does not silently estimate VO₂.

Common Fick errors

  • Using oxygen saturation percentages as though they were oxygen content values.
  • Using a peripheral venous sample instead of a true mixed venous pulmonary-artery sample.
  • Mixing mL/dL and mL/L without applying the conversion factor.
  • Calculating during a rapidly changing, non-steady physiological state.

Echo Cardiac Output From LVOT Diameter and VTI

Doppler echocardiography treats the LVOT stroke volume as the volume of a cylinder. The LVOT cross-sectional area is multiplied by the velocity time integral—the distance a column of blood travels during systole.

1LVOT areaπ × (diameter ÷ 2)²
2Stroke volumeLVOT area × VTI
3Cardiac outputSV × HR ÷ 1,000

With a 2.0 cm LVOT diameter and 20 cm VTI, area is 3.14 cm² and stroke volume is approximately 62.8 mL. At 72 beats/min, cardiac output is approximately 4.52 L/min.

Measurement quality matters. LVOT diameter and pulsed-wave Doppler VTI should be sampled at corresponding locations. Rhythm variation, Doppler alignment, outflow obstruction, shunts, and valve disease can affect interpretation.

Cardiac Output vs Cardiac Index

Absolute flow

Cardiac output

Liters of blood pumped per minute. Body size is not included.

CO = L/min
Body-size adjusted

Cardiac index

Cardiac output divided by body surface area.

CI = CO ÷ BSA

This page uses the Mosteller formula when height and weight are supplied: BSA = √[(height in cm × weight in kg) ÷ 3,600]. A commonly cited resting adult cardiac index reference is approximately 2.5–4.0 L/min/m², but method, age, physiological state, and clinical context matter.

What Is a Normal Cardiac Output?

A commonly quoted resting adult cardiac output is approximately 4–8 L/min. It is not a universal diagnostic range: a larger person may require more absolute flow, and cardiac output normally changes with exercise, fever, pregnancy, stress, medications, preload, afterload, and heart rate.

Do not interpret CO in isolation. Blood pressure, perfusion, lactate, urine output, oxygen delivery, examination, cardiac index, and changes over time may be more informative than a single calculated value.

Limitations of Cardiac Output Calculations

  • Different methods are not interchangeable: Fick, echo, and thermodilution can produce different results.
  • Input error propagates: especially LVOT diameter because it is squared.
  • Irregular rhythm: beat averaging may be required during atrial fibrillation or ectopy.
  • Changing physiology: results may become outdated quickly in unstable patients.
  • Fick assumptions: accurate VO₂ and paired arterial/mixed-venous samples are essential.
  • Population scope: this page does not provide fetal or pediatric reference interpretation.

Cardiac Output Calculator FAQs

How do you calculate cardiac output from heart rate?

You also need stroke volume. Multiply heart rate by stroke volume and divide by 1,000 to obtain L/min.

What is the Fick formula for cardiac output?

CO equals oxygen consumption divided by the arterial–mixed venous oxygen content difference, with unit conversion applied. Measured and assumed oxygen consumption should be clearly distinguished.

How do you calculate cardiac output using LVOT VTI?

Calculate LVOT area from diameter, multiply by LVOT VTI for stroke volume, then multiply stroke volume by heart rate and divide by 1,000.

What is cardiac index?

Cardiac index is cardiac output divided by body surface area, reported in L/min/m².

Is cardiac output the same as stroke volume?

No. Stroke volume is blood ejected per beat; cardiac output is blood pumped per minute.

Is cardiac output the same as ejection fraction?

No. Ejection fraction is a percentage ejected per beat, while cardiac output is volume per minute.

Can blood pressure alone calculate cardiac output?

No reliable universal equation derives cardiac output from blood pressure alone because vascular resistance, compliance, and other factors vary.

Can this calculator diagnose low-output shock?

No. Shock is a clinical diagnosis requiring assessment and validated measurements; an online calculation cannot establish it.

Sources and Editorial Notes

  1. ACC/AHA/ASE Key Data Elements and Definitions for Transthoracic Echocardiography.
  2. ASE/EACVI Recommendations for Cardiac Chamber Quantification.
  3. NCBI Bookshelf: Calculating Fick Cardiac Output and Input.
  4. Normative Reference Values of Cardiac Output by Pulsed-Wave Doppler Echocardiography.

Published and formula-checked July 15, 2026 by the Heart Score Calculator editorial team. No unverified clinician reviewer is claimed.