What is ejection fraction?
If you have had an echocardiogram, your report will contain a number labelled “Ejection Fraction” or “EF”. This single percentage is one of the most important measurements of how well your heart is working. It tells your doctor what proportion of blood is pumped out of the heart’s main pumping chamber — the left ventricle — with each heartbeat.
A healthy heart does not empty completely with every contraction. A certain volume of blood always remains in the ventricle. The ejection fraction represents the percentage that is pumped out, and this number gives clinicians a reliable snapshot of your heart’s pumping strength.
While ejection fraction is most commonly measured for the left ventricle (left ventricular ejection fraction, or LVEF), it can also be assessed for the right ventricle (RVEF), which pumps blood to the lungs. Throughout this guide, “ejection fraction” refers to LVEF unless stated otherwise.
How ejection fraction is calculated
The ejection fraction formula is straightforward. It equals the stroke volume (the amount of blood pumped out per beat) divided by the end-diastolic volume (the total amount of blood in the ventricle just before it contracts), multiplied by 100 to express it as a percentage.
For example, if the left ventricle holds 120 ml of blood at the end of diastole and pumps out 78 ml with each contraction, the ejection fraction is 65%. That falls within the normal range. The sonographer performing your echocardiogram calculates this automatically using the ultrasound machine’s built-in software.
What is a normal ejection fraction?
In the UK, sonographers and cardiologists use the categories recommended by the British Society of Echocardiography (BSE), published in their 2020 guideline on normal reference intervals for cardiac dimensions and function. [1]
| BSE Category | LVEF Range | What It Means |
|---|---|---|
| Normal | ≥55% | Your heart’s pumping function is normal. With each beat, 55% or more of the blood in the left ventricle is ejected to the body. |
| Borderline low | 50–54% | Pumping function is at the lower end of the normal range. This may be normal for you, or it could represent an early change. The BSE recommends further assessment — including LV volumes, tissue Doppler, and clinical history — before classifying the result as normal or abnormal. |
| Impaired | 36–49% | Your heart’s pumping function is reduced. An EF below 50% falls three standard deviations below the population mean, making it exceptionally unlikely to be a normal finding. The BSE uses the single term “impaired” and discourages the older labels of “mild” or “moderate” reduction. |
| Severely impaired | ≤35% | Pumping function is significantly reduced. This threshold is clinically important: in UK practice, device therapy (CRT, ICD) and specific heart failure medications are indicated when the EF is 35% or below. |
Why the BSE chose ≤35% as “severely impaired”: A large body of evidence demonstrates that therapeutic drugs and device therapies for heart failure have prognostic value specifically when LVEF is 35% or below. This includes ACE inhibitors, beta-blockers, mineralocorticoid receptor antagonists, and cardiac resynchronisation therapy. The BSE chose this threshold for clinical utility, providing a clear decision point for clinicians and sonographers. [1]
These categories apply equally to men and women. The BSE found that the absolute difference in EF between sexes is clinically insignificant — less than 1% — and well within the accepted inter-operator variability of echocardiographic EF measurements, which is often in the order of 5%.
How is ejection fraction measured?
Several imaging methods can measure ejection fraction, but the echocardiogram is the most common and widely accessible.
Echocardiogram (the standard method)
During a transthoracic echocardiogram (TTE), the sonographer places an ultrasound probe on your chest and obtains images of the left ventricle from two different angles: the apical four-chamber view and the apical two-chamber view. At each angle, the inner border of the left ventricle is traced at two points in the cardiac cycle — end-diastole (when the ventricle is at its fullest) and end-systole (just after it has finished squeezing). The machine then uses a calculation called the biplane Simpson’s method (also known as the method of discs) to determine the volume at each point and derive the ejection fraction. [1]
The biplane Simpson’s method is the recommended standard for 2D echocardiographic EF assessment. It is more accurate than visual estimation alone and provides a reproducible, quantitative result that can be tracked over time.
For a full guide to the echocardiogram procedure, what to expect, and how to prepare, see: What is an ultrasound echo?
Other measurement methods
| Method | How It Works | When It Is Used |
|---|---|---|
| Cardiac MRI (CMR) | Uses magnetic fields and radio waves to create highly detailed 3D images of the heart. Considered the “gold standard” for EF accuracy. | When echocardiographic image quality is poor, or when precise EF measurement is needed for treatment decisions (e.g., device implantation). |
| Cardiac CT | Uses X-ray technology to create cross-sectional images of the heart. | Less commonly used for EF alone; more often used to assess coronary arteries. See our upcoming guide: Echo vs CT. |
| MUGA scan | A nuclear medicine test that uses a small amount of radioactive tracer to track blood flow through the heart. | Monitoring EF during chemotherapy, where serial precision is needed to detect cardiotoxicity. |
| Cardiac catheterisation | A thin tube is inserted into the heart via a blood vessel, and contrast dye is injected to visualise the ventricle (ventriculography). | Invasive; used when catheterisation is already being performed for another reason (e.g., coronary angiography). |
Ejection fraction and heart failure classification
Heart failure is classified into three types based on ejection fraction. This classification, used by the European Society of Cardiology (ESC) and reflected in NICE guideline NG106, determines which treatments are recommended. [2]
| Heart Failure Type | Abbreviation | LVEF | What It Means |
|---|---|---|---|
| Heart failure with reduced ejection fraction | HFrEF | ≤40% | The heart muscle is weakened and cannot pump blood effectively. This is the type of heart failure with the strongest evidence base for drug and device therapy. |
| Heart failure with mildly reduced ejection fraction | HFmrEF | 41–49% | Pumping function is mildly reduced. Emerging evidence suggests that some heart failure medications may also benefit this group. |
| Heart failure with preserved ejection fraction | HFpEF | ≥50% | The heart pumps normally, but it is stiff and does not relax properly between beats. The ventricle fills with less blood, and symptoms of heart failure can still occur. This is sometimes called “diastolic heart failure”. |
A normal ejection fraction does not rule out heart failure. Some patients experience breathlessness, fatigue, and fluid retention despite having an EF of 50% or above. This is HFpEF — and it accounts for roughly half of all heart failure diagnoses. [3]
Have you noticed that the BSE and ESC use slightly different thresholds? The BSE defines “impaired” as 36–49% for echocardiographic reporting purposes, while the ESC splits this range into HFrEF (≤40%) and HFmrEF (41–49%) for treatment decisions. Both systems are correct — they serve different clinical purposes. Your cardiologist will use the ESC/NICE classification to guide your treatment plan.
What causes a low ejection fraction?
A reduced ejection fraction means the heart muscle is not contracting as forcefully as it should. Any condition that damages, weakens, or stiffens the heart muscle can lead to a drop in EF. The most common causes include:
- Coronary artery disease and heart attack: A heart attack damages a section of the heart muscle, and the scarred tissue can no longer contract. This is the most common cause of reduced EF in the UK.
- Dilated cardiomyopathy: The left ventricle becomes enlarged and stretched, reducing its ability to squeeze effectively. This can be inherited, caused by alcohol, viral infection, or sometimes has no identifiable cause (idiopathic).
- Hypertensive heart disease: Years of high blood pressure force the heart to work harder. Over time, the muscle thickens and then weakens.
- Heart valve disease: Severe valve regurgitation or stenosis places a chronic volume or pressure load on the ventricle, which can eventually lead to reduced function.
- Myocarditis: Inflammation of the heart muscle, often triggered by a viral infection, can temporarily or permanently reduce EF.
- Cardiotoxicity: Certain chemotherapy drugs (such as anthracyclines and trastuzumab) can damage the heart muscle. EF is monitored before, during, and after treatment.
- Arrhythmias: Prolonged rapid heart rhythms (such as uncontrolled atrial fibrillation) can weaken the heart muscle over time — a condition called tachycardia-induced cardiomyopathy.
For a detailed guide to the conditions echocardiography can identify, see: Heart conditions diagnosed by echocardiography.
Symptoms of a low ejection fraction
When the ejection fraction drops, the body may not receive the oxygen-rich blood it needs. The heart tries to compensate by beating faster, enlarging, or retaining fluid — but these mechanisms eventually fail. The symptoms that follow are the hallmarks of heart failure:
- Breathlessness (dyspnoea): Initially during physical activity, and in more advanced cases, at rest or when lying flat (orthopnoea). Some patients wake at night gasping for air (paroxysmal nocturnal dyspnoea).
- Fatigue and weakness: A persistent feeling of tiredness that does not improve with rest, caused by reduced blood flow to the muscles.
- Swelling (oedema): Fluid retention in the legs, ankles, feet, or abdomen. Rapid weight gain over a few days can indicate worsening fluid overload.
- Palpitations: A sensation of a rapid, fluttering, or irregular heartbeat.
- Reduced exercise tolerance: Activities that were once easy become difficult or impossible.
Some people with a mildly reduced EF (50–54% or even 36–49%) may have no symptoms at all. The echocardiogram can detect reduced function before symptoms appear, which is why screening is valuable for patients at risk.
Can ejection fraction be too high?
An ejection fraction above 75% is uncommon and can sometimes indicate a problem. It is most often seen in hypertrophic cardiomyopathy (HCM), a condition where the heart muscle is abnormally thick. The thickened walls make the left ventricular cavity smaller, so the heart empties a very high proportion of its (reduced) volume with each beat. The EF number looks high, but the actual volume of blood pumped out may be normal or even low. [3]
A very high EF can also occur in severe mitral regurgitation, where blood leaks backward into the left atrium during contraction. The ventricle appears to empty efficiently, but a significant portion of the ejected blood is going in the wrong direction.
Can a low ejection fraction be improved?
For many patients, the answer is yes. The degree of improvement depends on the underlying cause, how early treatment begins, and how well the patient responds to therapy. The goal is to reduce strain on the heart, improve its efficiency, and prevent further damage.
Medications
Guideline-directed medical therapy (GDMT) for heart failure with reduced ejection fraction includes four main classes of medication, each of which has been shown to improve survival and, in many cases, improve EF over time. [2]
| Drug Class | Examples | How It Helps |
|---|---|---|
| ACE inhibitors / ARBs / ARNI | Ramipril, candesartan, sacubitril-valsartan | Reduce the workload on the heart by lowering blood pressure and preventing harmful remodelling of the heart muscle. |
| Beta-blockers | Bisoprolol, carvedilol | Slow the heart rate, reduce oxygen demand, and allow the heart to fill more effectively. |
| Mineralocorticoid receptor antagonists (MRAs) | Spironolactone, eplerenone | Block the effects of aldosterone, reducing fluid retention and preventing fibrosis of the heart muscle. |
| SGLT2 inhibitors | Dapagliflozin, empagliflozin | Originally developed for diabetes, these drugs reduce heart failure hospitalisations and improve outcomes regardless of whether the patient has diabetes. |
Device therapy
For patients with a severely impaired EF (≤35%) who remain symptomatic despite optimal medication, device therapy may be recommended:
- Cardiac Resynchronisation Therapy (CRT): A specialised pacemaker that coordinates the contraction of both ventricles, improving pumping efficiency. CRT can lead to significant improvements in EF.
- Implantable Cardioverter Defibrillator (ICD): Monitors the heart rhythm and delivers a shock if a life-threatening arrhythmia is detected. It does not directly improve EF but reduces the risk of sudden cardiac death.
Lifestyle changes
Lifestyle modifications work alongside medical therapy and can have a meaningful impact on heart function and quality of life:
- Cardiac rehabilitation: A structured programme of supervised exercise, education, and psychological support. Ask your GP or cardiologist for a referral.
- Maintaining a healthy weight: Excess weight increases the workload on the heart.
- Reducing salt intake: Sodium promotes fluid retention, which worsens heart failure symptoms.
- Stopping smoking: Smoking damages blood vessels and increases the risk of coronary artery disease.
- Limiting alcohol: Excessive alcohol consumption can directly damage the heart muscle (alcoholic cardiomyopathy).
Your echocardiogram at Sonoworld
At Sonoworld, every echocardiogram is performed by a specialist consultant sonographer with over 20 years of clinical experience. The examination follows a systematic protocol that includes a full assessment of left ventricular size, wall thickness, regional wall motion, and — of course — ejection fraction using the biplane Simpson’s method.
Your report will include your EF percentage alongside the BSE category (normal, borderline low, impaired, or severely impaired), together with all supporting measurements: left ventricular volumes, tissue Doppler velocities (s′, e′), diastolic function grading, and valve assessments. This comprehensive report is provided to you on the same day and, with your consent, sent directly to your GP or referring cardiologist.
Are you concerned about your heart function? Have you been told your EF is low and want a follow-up assessment? Or do you simply want peace of mind? An echocardiogram at Sonoworld provides the answers you need — without a long NHS wait.
Book your echocardiogram
No GP referral required. Same-day and next-day appointments available at our Marylebone clinic. Self-pay and insured patients accepted.
Frequently asked questions
What is a normal ejection fraction?
What does a low ejection fraction mean?
How is ejection fraction measured?
Can ejection fraction be improved?
What is the difference between HFrEF, HFmrEF, and HFpEF?
Do I need a GP referral for an echocardiogram at Sonoworld?
References
- Harkness, A. et al. (2020). “Normal reference intervals for cardiac dimensions and function for use in echocardiographic practice: a guideline from the British Society of Echocardiography.” Echo Research and Practice, 7(1), G1–G18. PMC7040881
- National Institute for Health and Care Excellence (2018). “Chronic heart failure in adults: diagnosis and management.” NICE guideline NG106. nice.org.uk/guidance/ng106
- Cleveland Clinic (2022). “Ejection Fraction: What It Is, Types and Normal Range.” my.clevelandclinic.org
