Left ventricular ejection fraction (LVEF) is measured by calculating the percentage of blood your heart’s main pumping chamber pushes out with each beat. The formula is straightforward: LVEF equals stroke volume divided by end-diastolic volume, multiplied by 100. In practical terms, a doctor measures how much blood fills the left ventricle when it relaxes, how much remains after it contracts, and calculates the difference. A normal LVEF falls between 55% and 70%. What varies is the imaging method used to capture those volumes.
The Basic Formula
LVEF is expressed as a percentage using this calculation: LVEF (%) = (EDV − ESV) / EDV × 100. EDV is end-diastolic volume, the amount of blood in your left ventricle when it’s fully relaxed and filled. ESV is end-systolic volume, the blood left behind after the ventricle contracts. The difference between these two numbers is your stroke volume, the amount actually pumped out per beat.
If your left ventricle holds 120 mL of blood when full and 50 mL remains after contraction, your stroke volume is 70 mL and your LVEF is about 58%, which is normal. The challenge is getting accurate measurements of those volumes, and that’s where different imaging techniques come in.
Echocardiography: The Most Common Method
A standard echocardiogram (ultrasound of the heart) is the most widely used tool for measuring LVEF. The American Society of Echocardiography recommends a specific technique called the modified Simpson’s method, also known as the biplane method of disks. A sonographer places an ultrasound probe on your chest and captures two views of your heart from below: an apical four-chamber view and a two-chamber view.
In each view, the inner border of the left ventricle is traced at two moments: when the chamber is fully expanded and when it’s fully contracted. Software then slices the traced cavity into roughly 20 disk-shaped segments, calculates the volume of each one, and adds them up to estimate total volume at both points. From there, the LVEF formula does the rest. This approach replaced older geometric methods that assumed the left ventricle had a uniform shape, which it often doesn’t, especially in people with heart disease. The Simpson’s method handles irregular shapes more accurately because it measures actual contours rather than relying on mathematical shortcuts.
One limitation is that echocardiographic LVEF measurements carry some observer-to-observer variability. When two trained readers independently trace the same images using Simpson’s method, their results are generally close but not identical. The variability increases when image quality is poor, which can happen in patients with obesity, lung disease, or difficult body positioning. In some cases, clinicians skip the tracings entirely and estimate LVEF visually, a technique called “eyeballing.” Visual estimation can be surprisingly accurate in experienced hands, with studies showing average differences of less than 1% compared to formal measurements when the heart is functioning normally. But this method has a reported variability of up to plus or minus 14% between observers, making it less reliable for tracking subtle changes over time.
Cardiac MRI: The Gold Standard
Cardiac magnetic resonance imaging is considered the gold standard for LVEF measurement. The reason is its volumetric approach: instead of estimating volumes from two flat images (as echocardiography does), cardiac MRI captures a full stack of cross-sectional slices through the heart. This makes it far more accurate for ventricles that are misshapen or have regions of wall motion abnormality, as commonly seen after a heart attack.
During the scan, you lie inside an MRI machine for roughly 30 to 60 minutes while the scanner captures images synchronized to your heartbeat. No radiation is involved. You can take your usual medications beforehand with water, and no special preparation is typically needed for a standard cardiac MRI. You’ll change into a hospital gown and need to hold still, sometimes holding your breath briefly when instructed. Cardiac MRI is more expensive and less available than echocardiography, so it’s typically reserved for cases where echo images are inconclusive or when very precise tracking is clinically important.
Nuclear Imaging: The MUGA Scan
A multigated acquisition (MUGA) scan uses a small amount of radioactive tracer mixed with your own blood to measure LVEF. A blood sample is drawn, labeled with the tracer, and reinjected. After about 15 to 20 minutes for the tracer to circulate evenly, a gamma camera captures images of your heart synchronized to your ECG signal, collecting at least 16 images per heartbeat cycle. The entire exam takes roughly 30 minutes of imaging across multiple camera angles.
MUGA scans have largely fallen out of routine use in favor of echocardiography, but they remain important in one specific situation: monitoring patients on certain chemotherapy drugs. Anthracycline chemotherapies (such as doxorubicin) can damage the heart, and MUGA provides highly reproducible LVEF measurements that allow oncologists to detect even small drops in heart function between treatment cycles. Guidelines call for a baseline MUGA before starting these drugs, with repeat scans at specific dose thresholds. If LVEF drops below 30% at any point, the chemotherapy is stopped. If it falls between 30% and 50%, a MUGA is performed before every subsequent dose.
CT and PET-Based Measurement
Cardiac CT can also estimate LVEF, though it’s rarely ordered for that purpose alone. CT scans involve radiation and contrast dye, so they’re typically used when a scan is already being done for another reason, such as evaluating coronary arteries, and LVEF data is extracted as a bonus. The scanner captures images at multiple phases of the heartbeat, allowing software to calculate volumes at end-diastole and end-systole much like other methods.
PET/CT scanning is an emerging approach, particularly using first-pass imaging where the tracer is captured as it initially flows through the heart chambers. Early studies using ultra-sensitive digital PET scanners show LVEF values very close to MRI results, but the technique requires specialized equipment and software that isn’t yet standard in most facilities.
What the Numbers Mean
An LVEF between 55% and 70% is normal. This means your heart is pumping out more than half of the blood in the left ventricle with each beat. An LVEF of 41% to 49% is considered mildly reduced, suggesting the heart isn’t contracting as forcefully as expected.
An LVEF at or below 40% typically indicates heart failure with reduced ejection fraction (HFrEF), the classic form of heart failure where the heart muscle has weakened. An LVEF of 50% or above, when combined with heart failure symptoms like shortness of breath and fluid retention, points to heart failure with preserved ejection fraction (HFpEF), a condition where the heart pumps adequately but doesn’t relax and fill properly.
These thresholds matter because they guide treatment decisions. Many heart failure medications have been studied specifically in patients with LVEF at or below 40%, so your number directly influences which therapies your cardiologist recommends. It’s also why accuracy and consistency in measurement matter. A difference of a few percentage points can shift a diagnosis from one category to another, which is one reason clinicians may repeat measurements or use cardiac MRI when echocardiographic results are borderline or unclear.
Which Method Your Doctor Will Likely Use
For most people, the first LVEF measurement will come from a standard transthoracic echocardiogram. It’s noninvasive, widely available, involves no radiation, and takes about 30 to 45 minutes. If echo images are poor quality or results seem inconsistent with your symptoms, cardiac MRI is the next step. MUGA scans are reserved primarily for chemotherapy monitoring, and CT-based measurement is usually opportunistic rather than the primary goal of the scan.
If you’re having serial measurements to track heart function over time, using the same imaging method and ideally the same facility each time reduces variability and gives your doctor the clearest picture of any real changes.