Echo Cardiac Output Calculator (LVOT Method)
Enter values from transthoracic echo. Diameter and VTI should both be measured at the LVOT.
What this cardiac output echo calculator does
This calculator estimates cardiac output (CO) using standard Doppler echocardiography inputs: LVOT diameter, LVOT velocity-time integral (VTI), and heart rate. The method is based on stroke volume flow through the left ventricular outflow tract.
It can also estimate cardiac index (CI) if body surface area (BSA) is provided. Cardiac index is often more useful than raw output because it normalizes flow to patient size.
Formula used
The calculator applies the classic LVOT flow equations:
Stroke volume (mL/beat) = LVOT area × LVOT VTI
Cardiac output (L/min) = Stroke volume × Heart rate / 1000
Cardiac index (L/min/m²) = Cardiac output / BSA
How to measure each input correctly
1) LVOT diameter
Measured in parasternal long-axis view, usually in mid-systole from inner-edge to inner-edge at the base of the aortic valve. Because diameter is squared in the formula, small errors in diameter can significantly shift the final cardiac output.
2) LVOT VTI
Obtained with pulsed-wave Doppler in apical 5-chamber or long-axis view, placing sample volume at the LVOT. Trace the spectral envelope carefully. Beat averaging is recommended when rhythm irregularity is present.
3) Heart rate
Use the heart rate at the time of VTI acquisition. If rate variability is significant, average multiple beats.
4) Body surface area (optional)
Include BSA when you want cardiac index for hemodynamic interpretation adjusted to patient size.
Interpreting results
- Stroke volume: amount ejected per beat (mL/beat).
- Cardiac output: total flow per minute (L/min).
- Cardiac index: cardiac output normalized for body size (L/min/m²).
Typical resting adult cardiac output is often around 4.0 to 8.0 L/min, and cardiac index commonly around 2.2 to 4.0 L/min/m². These are general reference ranges and should always be interpreted in clinical context (temperature, loading conditions, medications, sepsis, valvular disease, and technical quality).
Common pitfalls in echo-derived cardiac output
- Diameter error: the largest source of uncertainty due to the squared effect.
- Poor Doppler alignment: underestimates VTI when beam-flow angle is suboptimal.
- Incorrect sample volume placement: can capture non-LVOT velocities.
- Irregular rhythm: single-beat measures can be misleading.
- Dynamic physiologic state: values can shift rapidly with preload/afterload changes.
Example calculation
If LVOT diameter is 2.0 cm, LVOT VTI is 20 cm, and heart rate is 70 bpm:
- LVOT area = π × (1.0)² = 3.14 cm²
- Stroke volume = 3.14 × 20 = 62.8 mL/beat
- Cardiac output = 62.8 × 70 / 1000 = 4.40 L/min
If BSA = 1.9 m², then cardiac index = 4.40 / 1.9 = 2.32 L/min/m².
Clinical reminder
This tool is for educational and workflow support. It does not replace direct clinical judgment, invasive hemodynamics when indicated, or formal echocardiography interpretation by qualified professionals.