Low voltage QRS on an electrocardiogram (ECG) means the electrical signals produced by your heart’s contractions are registering as unusually small on the tracing. By traditional standards, this is diagnosed when the tallest QRS deflection in every limb lead measures less than 0.5 millivolts, or less than 1.0 millivolt in every chest lead. The finding can reflect something as benign as extra body fat insulating the signal, or it can point toward serious heart disease, lung disease, or fluid buildup around the heart. Because the same reading can mean very different things depending on context, understanding the full range of causes is what separates a worrisome finding from a harmless one.
How Low QRS Voltage Is Defined
The QRS complex is the spiky part of each heartbeat on an ECG tracing, representing the electrical wave that triggers the main pumping chambers to contract. Doctors have traditionally used a fixed threshold: if the peak-to-trough voltage in every limb lead stays below 0.5 mV, or below 1.0 mV across all six chest leads, the ECG is labeled “low voltage.” These cutoffs have been in clinical use for decades, and most hospitals still apply them.
Those thresholds, however, were not designed with sex differences in mind. A 2024 study analyzing a large dataset proposed that sex-specific cutoffs would be more accurate, suggesting minimum limb-lead amplitudes of roughly 0.87 mV for men and 0.74 mV for women, and minimum chest-lead amplitudes of about 1.54 mV for men versus 0.96 mV for women.1ScienceDirect. Should ECG criteria for Low QRS voltage (LQRSV) be specific for Sex? The idea is that using a single universal cutoff risks missing genuinely low voltage in men (whose normal amplitudes run higher) while over-diagnosing it in women (whose normal amplitudes are naturally lower). This remains an active area of debate, and the traditional thresholds are still the ones most clinicians use day to day.
Cardiac Causes
When low voltage originates from the heart itself, it usually signals that something is reducing the amount of healthy, electrically active heart muscle or interfering with how well that electrical activity reaches the body surface. Several cardiac conditions fit that description.
Cardiac Amyloidosis
Cardiac amyloidosis is one of the most recognized associations. In this disease, abnormal protein deposits infiltrate the heart muscle, stiffening it and replacing functional tissue. The classic clinical picture is a thickened heart wall on echocardiogram paired with low voltage on the ECG, a mismatch that serves as a diagnostic red flag for the condition.2PubMed. ECG/echo indexes in the diagnostic approach to amyloid cardiomyopathy: A head-to-head comparison from the AC-TIVE study In a study of over 400 patients with cardiac amyloidosis, low QRS voltages appeared in about 41% of the group, with a higher rate in the AL (light-chain) subtype than in the ATTR (transthyretin) subtype.3PubMed Central. Low QRS Voltages in Cardiac Amyloidosis: Clinical Correlates and Prognostic Value The paradox of a thick-walled heart producing a small electrical signal is a strong nudge toward amyloid as the underlying problem, and early suspicion can lead to earlier treatment.4PubMed Central. Paradoxical Left Ventricular Hypertrophy by Echocardiogram and Low Voltage ECG: A Key Clue in the Diagnostic Workup of Two Distinct Presentations of Cardiac AL Amyloidosis
Pericardial Effusion and Tamponade
Fluid collecting in the sac around the heart, called pericardial effusion, literally places an insulating layer between the heart and the ECG electrodes. The electrical signal has to pass through that fluid before it reaches the skin, and it gets attenuated in the process. When this is accompanied by a fast heart rate and a distinctive beat-to-beat alternation in QRS size (called electrical alternans), it raises concern for cardiac tamponade, a medical emergency where the fluid compresses the heart enough to impair its pumping.5PubMed. Electrical Alternans A case report illustrating this pattern described a patient whose ECG showed low voltage complexes and electrical alternans most prominently in the chest leads, leading directly to the diagnosis of pericardial effusion on ultrasound.6Resuscitation. A 45-year-old female presented to the emergency department with a 3 days history of worsening shortness of breath
Myocardial Infarction and Ischemic Heart Disease
A heart attack can destroy enough muscle to shrink the overall electrical signal. In one study of acute myocardial infarction patients, those with low voltage on their ECG had a higher rate of prior heart attacks, extensive current damage, congestive heart failure, and cardiogenic shock, suggesting the pattern reflects widespread loss of working heart muscle.7PubMed. Incidence and significance of the low-voltage electrocardiogram in acute myocardial infarction In patients presenting with a particular type of heart attack (anterior ST-elevation MI), low QRS voltage appeared in about one in five and independently predicted multi-vessel coronary disease, with roughly two and a half times the odds compared to patients with normal voltage.8PubMed. Low QRS Voltage on Presenting Electrocardiogram Predicts Multi-vessel Disease in Anterior ST-segment Elevation Myocardial Infarction
Myocarditis and Arrhythmogenic Cardiomyopathy
Inflammation of the heart muscle, or myocarditis, can also reduce QRS voltage. Experimental models of myocarditis showed that summed QRS voltage dropped significantly as myocardial necrosis peaked, reaching its lowest point about two weeks into the disease when tissue damage and organ congestion were most severe.9Journal of the American College of Cardiology. Electrocardiographic findings in experimental myocarditis in DBA/2 mice: complete atrioventricular block in the acute stage, low voltage of the QRS complex in the subacute stage and arrhythmias in the chronic stage Arrhythmogenic right ventricular cardiomyopathy (ARVC), a condition where heart muscle is progressively replaced by fatty and fibrous tissue, produces some of the lowest total QRS voltages seen among cardiac conditions, particularly in patients whose disease has advanced enough to require a heart transplant.10The American Journal of Cardiology. Usefulness of Total 12-Lead QRS Voltage for Diagnosis of Arrhythmogenic Right Ventricular Cardiomyopathy in Patients With Heart Failure Severe Enough to Warrant Orthotopic Heart Transplantation
Causes Outside the Heart
The ECG signal has to travel from the heart through surrounding tissues to the skin electrodes, and anything that increases the distance or electrical resistance along that path can dampen it. Several non-cardiac conditions do exactly that.
Obesity and Body Fat
Fat tissue has high electrical resistance, so carrying more of it between the heart and the electrodes naturally reduces the recorded voltage.11PubMed. Relation between body fat-corrected ECG voltage and ambulatory blood pressure in patients with essential hypertension This is one of the most common and least worrisome explanations for a low-voltage ECG. In clinical practice, obesity alone can push QRS amplitudes below the traditional cutoffs, which is one reason the finding always needs to be interpreted in the context of a patient’s body habitus.
Emphysema and COPD
In chronic obstructive pulmonary disease, particularly when emphysema is present, the lungs become hyperinflated and filled with air-trapping bullae. This creates multiple problems for ECG voltage. The air-filled spaces act as electrical insulators. The diaphragm flattens, pushing the heart downward and away from the standard chest electrode positions. The heart may also rotate in ways that direct its electrical forces away from the electrodes. On top of all that, left ventricular filling can be impaired, reducing the heart’s overall electrical output.12Open Heart. Mechanisms of ECG signs in chronic obstructive pulmonary disease The result is often a low-voltage ECG that improves if the patient’s lung condition is treated effectively.
Peripheral Edema and Pleural Effusion
Swelling from fluid retention anywhere in the body, regardless of the underlying cause, can produce reversible low voltage on the ECG. The extra fluid shortens signal amplitudes and even alters other ECG measurements like P-wave size and QT interval duration.13PubMed. Low QRS voltage and its causes Pleural effusion, fluid around the lungs rather than the heart, has a similar dampening effect. Left-sided pleural effusions, in particular, can reduce QRS amplitude in proportion to the volume of fluid present. When the effusion is drained, the voltage typically comes back up.
Hypothyroidism
Severe underactive thyroid function is a classic metabolic cause. Hypothyroidism can lead to pericardial effusion, which damps the signal, but thyroid hormone deficiency itself also appears to reduce ECG voltage independently. A study of hypothyroid patients with pericardial effusions found that low voltage improved after thyroid replacement therapy even when large effusions were still present, suggesting that the hormonal deficit contributes directly. Multi-variate analysis in that study linked low voltage to large pericardial effusion, patient age, and low thyroid hormone levels in combination.14PubMed. The cause of low voltage QRS complex in primary hypothyroidism. Pericardial effusion or thyroid hormone deficiency?
Why Sex, Age, and Ethnicity Affect Normal Ranges
QRS voltage is not the same across all healthy people. Men generally produce higher amplitudes than women, especially in the chest leads, and there is evidence that younger men have higher thresholds than older men.15Computers in Cardiology. Age and sex dependent criteria for lower limits of QRS voltages These differences matter because applying a single cutoff to everyone can label a healthy woman’s ECG as abnormal while missing a genuinely depressed signal in a larger man.
Ethnicity plays a role too. ECG amplitudes tend to be higher in Black individuals than in White individuals, while Hispanic populations show a more mixed pattern depending on the specific lead being measured. A study of North American men and women from three ethnic groups found that being overweight shifted the heart’s electrical axis and reduced some voltage measurements, and that these effects interacted with both age and race.16PubMed. Ethnic differences in ECG amplitudes in North American white, black, and Hispanic men and women. Effect of obesity and age A separate study of men from six different ethnic backgrounds working in Saudi Arabia confirmed significant differences in standard voltage measurements between groups, although the differences were less pronounced in women.17PubMed Central. Ethnic differences in electrocardiographic amplitude measurements
The practical takeaway is that a fixed voltage cutoff is a rough tool. It was developed in populations that did not fully represent the diversity of the people who now get ECGs. A clinician reading your ECG should consider your sex, body size, and ethnic background before deciding whether a borderline reading is truly abnormal.
What Low Voltage Means for Prognosis
Low voltage is not just a diagnostic signpost pointing toward a particular disease. It appears to carry prognostic weight in its own right. In people free of known cardiovascular disease, those with low QRS voltage had a mortality rate roughly twice that of those without it, amounting to about a 60% higher risk of death even after accounting for common risk factors like smoking, blood pressure, diabetes, and body mass index.18PubMed. Risk of mortality in individuals with low QRS voltage and free of cardiovascular disease That elevated risk was consistent across age groups, races, and sexes, suggesting it is not simply a proxy for one hidden condition.
In acutely ill hospitalized patients, low QRS voltage is an even stronger signal. A study of nearly 1,500 medical inpatients found that a combined lead I and lead II voltage below 1.8 mV was associated with roughly three and a half times the odds of dying in hospital. Strikingly, not a single patient who was mobile on admission and had voltages above that threshold died during their hospital stay.19PubMed Central. QRS voltage is a predictor of in-hospital mortality of acutely ill medical patients In patients with sepsis specifically, hospital mortality was about 50% in the low voltage group compared to about 28% in the normal voltage group, and low voltage independently predicted death with roughly two and a half times the odds.20Scientific Reports. Early detection of low QRS voltage and its association with mortality in patients with sepsis
These prognostic findings do not mean that low voltage itself causes harm. More likely, it acts as a barometer of the body’s overall physiological state, reflecting some combination of fluid shifts, tissue damage, metabolic derangement, and reduced cardiac function that standard blood tests and vital signs may not fully capture.
What Happens After a Low Voltage Finding
When low QRS voltage shows up on a routine ECG, the next step depends entirely on context. In an overweight person with no symptoms and no other ECG abnormalities, the finding alone may not require any additional testing. In a patient with unexplained shortness of breath, heart failure symptoms, or a thickened heart wall on ultrasound, it triggers a more focused investigation.
An echocardiogram is typically the first follow-up test. It can reveal pericardial effusion, wall thickening suggestive of amyloidosis, or reduced pump function. If amyloidosis is suspected, specialized blood tests and sometimes cardiac MRI or nuclear imaging are used to confirm the type. For emphysema or pleural effusion, imaging of the chest may be the more productive next step.
In young athletes, isolated low voltage poses a particular challenge. Most of the time it reflects normal variation or body composition, but in rare cases it can be the only surface clue to an underlying cardiomyopathy. Researchers have suggested that athletes with this finding should at minimum get an echocardiogram and an exercise ECG to look for ventricular arrhythmias. Because some forms of heart muscle disease, particularly those involving scarring, can be invisible on echocardiography, cardiac MRI may be warranted when there is a family history of cardiomyopathy or sudden cardiac death, additional ECG abnormalities like T-wave inversions, or exercise-induced arrhythmias.21PubMed Central. Prevalence and clinical significance of isolated low QRS voltages in young athletes
When Low Voltage Reverses
One underappreciated aspect of low QRS voltage is that in many cases it is reversible. Draining a pericardial or pleural effusion typically restores normal amplitudes. Treating hypothyroidism with replacement hormone can normalize the ECG even before a coexisting pericardial effusion resolves. Resolving peripheral edema from any cause, whether through diuretics, dialysis, or treating the underlying condition, brings amplitudes back up. Even weight loss in obese individuals can increase QRS voltage as the insulating fat layer thins.
This reversibility is clinically useful. If someone’s ECG was previously normal and new low voltage appears, comparing the two tracings can help narrow the timeline and identify a new problem like fluid accumulation or worsening thyroid function. Serial ECGs in hospitalized patients can also track response to treatment: rising QRS voltage after pericardial drainage or diuresis is a reassuring sign that the underlying cause is being addressed.
On the other hand, low voltage that persists despite treatment of reversible causes raises the suspicion of a structural problem in the heart itself, such as amyloid infiltration, fibrosis from a cardiomyopathy, or scarring from a prior infarction. In those cases, the signal reduction is permanent because the healthy muscle that generates the electrical activity has been replaced by tissue that does not conduct.
Signal-Averaged ECG and the Limits of Standard Recordings
Standard 12-lead ECGs are the workhorse for detecting low voltage, but they have limitations. Very small electrical signals at the tail end of the QRS complex, called late potentials, are invisible on a routine tracing because they are buried in background noise. Signal-averaged electrocardiography (SAECG) addresses this by mathematically combining hundreds of heartbeats from three orthogonal leads to cancel out random noise and reveal those tiny signals. The resulting filtered QRS complex can be measured for total duration, the amplitude of its terminal portion, and how long the slow-amplitude tail lasts.22PubMed Central. Signal‐averaged electrocardiography: Past, present, and future
Late potentials detected this way are associated with areas of scarred myocardium that conduct electricity slowly, creating a substrate for dangerous heart rhythms. SAECG has been used primarily in evaluating patients at risk for ventricular arrhythmias, particularly after a heart attack or in suspected ARVC. It is not a replacement for the standard ECG in detecting low voltage, but it adds a layer of information about the electrical health of the heart muscle that conventional recordings cannot provide. For patients whose low voltage hints at an underlying cardiomyopathy, SAECG can help determine whether abnormal slow-conduction zones are present, guiding decisions about further testing or treatment.