Start here: normal-looking but underperforming
The usual headline measure of heart function, the ejection fraction, captures how much blood the heart pumps out with each beat, and it can look perfectly normal while subtler aspects of the heart's function are off. The heart muscle can be squeezing slightly less effectively than it should without that showing up on the standard number.
This matters for the many people with persistent breathlessness whose echocardiogram is read as normal. A normal ejection fraction does not fully exclude a problem with how the heart muscle is actually working.
What strain imaging adds
Global longitudinal strain is a more sensitive measure derived from the same ultrasound images. Instead of how much blood is ejected, it measures how much the heart muscle fibres actually shorten as they contract, picking up subtle weakness that ejection fraction misses.
In people with persistent breathlessness after COVID, reduced strain has been found even after overt heart and lung disease is excluded, suggesting a subclinical impairment in the muscle's performance.1 It is a finer-grained look at a heart that the coarser measure calls normal.
low-moderateemergingimaging; normal standard tests
The test-mismatch pattern
This is another of long COVID's test-mismatch findings, where a sensitive measure is abnormal while the standard ones are normal. It sits alongside the impaired gas transfer seen on specialised lung imaging: in both, the routine test reassures while a finer measure detects a real problem.
Recognising the pattern is useful. When breathlessness persists despite normal standard tests, the question is not whether something is wrong but whether the right, sensitive measure has been used to look for it.
test-mismatchsensitive measure abnormal
What it might mean
Reduced strain points to the heart muscle as one possible contributor to persistent breathlessness, distinct from the autonomic and breathing-pattern causes that explain much of it. It could reflect subtle inflammation, microvascular involvement, or strain from working against an abnormal circulation.
The grade is low-to-moderate and emerging, so this is a real but not fully established finding. It identifies a subset whose breathlessness has a cardiac component, without yet explaining exactly why the strain is reduced or how often it matters clinically.
Where it fits among the causes
Breathlessness after COVID has several possible drivers: breathing pattern disorder, autonomic dysfunction, impaired gas transfer, and, in some, this subclinical cardiac strain. Most breathlessness is not primarily cardiac, so strain is one contributor to weigh, not the leading explanation.
Its value is in completing the picture for the subset where the heart is involved. Matching the treatment to the actual driver matters, and knowing that a sensitive cardiac measure can be abnormal helps ensure a cardiac contribution is not missed when it is present.
What it means in practice
Strain imaging is available in many echocardiography labs but is not always reported routinely, so part of the practical value is knowing it exists. For persistent breathlessness with a normal standard echo, it can be reasonable to ask whether strain was assessed.
There is no specific treatment aimed at the strain finding itself; management follows the broader cause and any standard cardiac care a clinician advises. The finding mainly helps explain and validate breathlessness that the usual tests call normal.
What we don't know
Honest about the edges of the evidence. These are open questions, not settled answers.
- How often reduced strain is present in persistent post-COVID breathlessness.
- What actually causes the reduced strain, inflammation, microvascular injury, or load.
- Whether the strain abnormality improves as people recover.
- Whether it predicts any longer-term cardiac outcome.
- How to sequence strain imaging against autonomic and breathing-pattern assessment.
- Whether any treatment changes the strain finding or the symptoms it tracks.
What this means for you
If you are breathless and your standard heart scan was read as normal, it is worth knowing that a more sensitive measure, global longitudinal strain, can sometimes pick up subtle weakness the usual number misses. A normal ejection fraction does not fully rule out a cardiac contribution.
Most post-COVID breathlessness is not primarily cardiac, so this is one contributor to weigh rather than the likely answer. Where breathlessness persists despite a normal standard echo, asking whether strain was assessed is reasonable, while keeping the autonomic and breathing-pattern causes, which explain more of it, firmly in view.
Keep the proportions right as you take this forward. A sensitive strain measure can reveal a subtle cardiac contribution that the standard echo misses, which is genuinely worth asking about when breathlessness persists. But most post-COVID breathlessness is driven by breathing pattern and autonomic dysfunction rather than the heart, so treat strain as one box to check among several, not the explanation to fixate on. Where the heart is genuinely involved, finding it matters; where it is not, chasing it can distract from the breathing-pattern and autonomic causes that, for most people, more often hold the real answer for post-COVID breathlessness.
References
Each reference links to the source on PubMed, PMC, or the publisher.