What Is Global Longitudinal Strain in Cardiology?

Global longitudinal strain, usually shortened to GLS on an echo report, measures how strongly the heart muscle squeezes along its length with each beat. Software calculates it from the same ultrasound images used in a standard heart scan. GLS is increasingly reported alongside ejection fraction because it tends to show early trouble in the heart muscle while the pumping still looks normal.¹

What GLS Actually Measures

An echocardiogram, or echo, is an ultrasound scan of the heart. GLS is usually measured on the left ventricle, the main pumping chamber. Software follows tiny speckle-like patterns in the muscle on the image and measures how the wall deforms in three directions: lengthwise, around, and inward.² “Strain” is simply the percentage the muscle shortens compared with its relaxed length. “Global” means the result averages the whole chamber wall, and “longitudinal” means the lengthwise direction from the valves toward the tip.

Muscle that shortens by a fifth of its relaxed length has a strain of about 20%. In the heart, the wall shortens from base to tip on each squeeze, and the software tracks many small points along the wall through the beat.

Shortening is recorded as a negative change, so a healthy heart shows a minus sign. A more negative number, like -20%, means stronger shortening than -14%. Doctors often speak of the absolute value, so “18%” and “-18%” mean the same thing. A lower absolute value means weaker muscle.

Lengthwise shortening is also often the first motion to suffer. The inner layer of heart muscle has fibers running mostly lengthwise.³ That inner layer is the first to be starved when blood flow drops, so lengthwise strain worsens earlier than the other directions.⁴

Normal GLS Values and What Shifts Them

The range is wide because healthy hearts truly differ, and because measurement methods differ between labs and machines. Falling within the range also doesn’t guarantee your heart is unchanged; a drop from your personal baseline can still matter, as the cancer section explains.

Age and sex move the range. On echo, healthy values become slightly less negative with age.⁹ Women tend to have more negative, stronger values than men.¹⁰ On heart MRI, though, lengthwise strain did not change with age in healthy adults.¹¹ So a borderline value in an older man may mean something different than in a young woman.

A value like -17% sits at the edge and is rarely interpreted alone. Doctors weigh symptoms, other echo findings, and prior scans, and a single borderline number is a reason for follow-up, not alarm. Cutoffs vary slightly between labs, so it’s reasonable to ask which one yours uses.

When you look at your own report, check whether it lists the lab’s reference range, since that is the one your doctor will use. Make sure you’re reading the left ventricle GLS line and not a right-ventricle or atrial value, which have different ranges. Also note whether the value is written as negative or as a plain percentage, because the same result may appear either way.

How GLS Differs From Ejection Fraction

Ejection fraction is the share of blood the main pumping chamber pushes out with each beat, normally about 50% to 70%. GLS looks at the muscle’s own shortening instead. A heart can keep a normal ejection fraction while its lengthwise shortening has already weakened,¹² so GLS picks up muscle problems earlier.¹³ It also adds information about future risk beyond what ejection fraction gives.¹⁴

The reason is that ejection fraction is a ratio of blood pumped out relative to blood filling the chamber. The heart can compensate for weak lengthwise shortening by squeezing harder in other directions, which keeps the overall output looking fine. That is one reason a person can have symptoms or early muscle damage with a normal ejection fraction on the report.

Both numbers appear because they do different jobs. Ejection fraction remains the standard for treatment decisions, while GLS refines the picture, especially when ejection fraction is normal.

GLS is also more consistent between readers. It gives more repeatable results than ejection fraction, whatever the operator’s training,¹⁵ partly because ejection fraction relies on tracing chamber outlines by eye, which varies between readers. GLS has also outperformed ejection fraction in estimating damage after a heart attack and in predicting dangerous rhythms and death.¹⁶

Two readers tracing the same heart can land several points apart on ejection fraction, which can hide a real change or create an imagined one. GLS still depends on image quality, so it is steadier, not perfect.

Why GLS Is Checked During Cancer Treatment

Ejection fraction has long been used to watch the heart during heart-toxic chemotherapy.¹⁷ But a fall in ejection fraction appears relatively late in the damage.¹⁸ An early relative drop of 10% to 15% from your own starting GLS is a useful early warning of later heart damage.¹⁹

That drop is relative to your own baseline, not absolute points. A baseline of -20% falling to about -17% is roughly a 15% decline. This is why a pre-treatment scan is so valuable, and why it helps to have scans done on the same machine for a fair comparison. In one reported case after doxorubicin, ejection fraction dipped only slightly to 55% while GLS dropped markedly to -16%.²⁰

Not every chemotherapy drug affects the heart, so monitoring is mainly for treatments known to carry that risk, such as anthracyclines like doxorubicin. Damage can build with the total dose over the course of treatment, which is why scans are repeated rather than done once. Catching a change early gives the team a chance to act before the heart is badly weakened.

Follow-up echoes are then scheduled during and after treatment, with timing depending on the drug, the dose, and the patient’s heart risk factors. If a baseline GLS was never recorded, later scans are harder to judge, so it is fair to ask whether GLS was measured at the start.

After a drop, the cancer and heart teams discuss the finding together. Options may include heart-protective medicines or closer monitoring. Treatment is not automatically stopped, because decisions weigh the cancer benefit too.

What an Abnormal GLS Means for Heart Conditions

In heart failure with preserved ejection fraction, about 6 in 10 patients had abnormal GLS.²¹ Those with abnormal GLS had more hospital admissions or deaths over about 4.6 years, 62% versus 44%.²² They were also about twice as likely to see their ejection fraction later decline.²³ In this condition, reduced GLS tracks with stiffer, scarred muscle and worse exercise ability.²⁴

In heart failure with reduced ejection fraction, each 1% worsening of GLS raised death risk by about 15%.²⁵ GLS predicted survival better than any other echo measure in that group.²⁶ After a heart attack, larger scarred areas go with weaker GLS,²⁷ and GLS tracks fairly closely with scar size measured by heart MRI.²⁸ Scarred muscle cannot shorten, so a bigger scar leaves less working muscle. Echo can therefore give a rough sense of how much muscle was lost without always needing an MRI, though MRI remains the more direct way to see and measure the scar itself.

GLS helps in other conditions too. A pattern where the tip of the heart moves well but the base does not suggests cardiac amyloidosis, a protein buildup in the muscle.²⁹ This pattern can be missed, so MRI may be needed to confirm.³⁰ In diabetes and obesity, GLS can show early muscle weakness before symptoms.³¹ In narrowed aortic valves without symptoms, GLS may help time valve repair.³² A low value supports a diagnosis rather than naming one; the cause has to be identified separately.

If your value is abnormal, a few questions help. Ask whether the change is new compared with older scans, and what condition the doctor thinks explains it. Ask whether treatment or a follow-up echo is planned, and whether an MRI or other test would add clarity.

Why Your GLS Can Vary Between Scans

The same hearts measured on nine different vendors’ systems gave average GLS from about 18% to 21.5%.³³ Switching machines alone can move your number by up to about 3.7 points.³⁴ Each manufacturer uses its own software to track the muscle and compute strain, so identical hearts can produce slightly different results. That is a measurement difference, not a sign that either machine is wrong. Comparing results from the same lab and machine whenever possible avoids the problem.

Image quality matters too. Strain software depends on clear images, and motion and fast breathing can degrade them.³⁵ Higher body weight can reduce image quality.³⁶ Fully automated software worked in 97% of scans and predicted outcomes as well as manual analysis.³⁷ Artificial-intelligence tools now measure GLS close to expert values.³⁸ When echo images are poor, heart MRI can also measure strain, though results aren’t interchangeable.³⁹

Even on the same machine, the result depends on exactly which images were recorded and how the software outlined the wall. A shift of a point or two between scans, with no new symptoms, is often within normal variation. A larger change, especially one that persists on repeat scans or matches symptoms, deserves more attention.

Strain Beyond the Left Ventricle

The right ventricle pumps blood to the lungs. Its wall is thinner than the left’s, which makes it harder to assess by eye on echo. Its shortening is mostly lengthwise too, so strain of its free wall captures its function well. That matters when lung pressure is high, since the right side must work harder against it.

In high blood pressure in the lungs, weaker right-ventricle free-wall strain predicts higher death risk regardless of cause.⁴⁰ A free-wall value weaker than about -20% was linked to higher death risk even when other standard measures looked normal.⁴¹ In severe tricuspid valve leakage, values of 18% or less signaled higher risk.⁴²

The free wall is the outer wall of the right ventricle, away from the wall it shares with the left side. The shared wall is partly driven by the left ventricle, so measuring only the free wall reflects the right side’s own effort. Reports may list both, so check which value a number refers to. Right-side values are usually labeled “RV free wall strain” or “RVFWLS.”

The upper chambers get the same treatment. Low left atrium strain, the upper chamber’s stretch, can point to hidden atrial fibrillation after unexplained stroke.⁴³ In atrial fibrillation, weaker atrial strain linked to higher stroke risk even with similar GLS.⁴⁴ Atrial strain is often listed as “LA reservoir strain” and is positive. Normal ranges differ from left-ventricle GLS, so don’t compare them directly.