Ejection fraction is the percentage of blood your heart pumps out with each beat. It’s the single most important number doctors use to gauge how well your heart is working as a pump. A normal ejection fraction falls between 50% and 75%, meaning your heart pushes out roughly half to three-quarters of its blood supply every time it contracts.
How Ejection Fraction Is Calculated
Your heart fills with blood between beats, then squeezes to push that blood out to the rest of your body. Ejection fraction measures the proportion of blood that actually leaves the heart’s main pumping chamber (the left ventricle) during each squeeze. If your left ventricle holds 100 milliliters of blood when full and pumps out 60 milliliters, your ejection fraction is 60%.
The number reflects how strong your heart muscle is. A higher percentage means more blood is being delivered to your organs and tissues with each beat. A lower percentage means your heart isn’t contracting forcefully enough to keep up with your body’s demands.
What the Numbers Mean
Ejection fraction is grouped into ranges that tell you and your doctor how your heart is performing:
- 50% to 75%: Normal. Your heart is pumping effectively.
- 40% to 49%: Mildly reduced. Pumping ability is slightly below normal. You may feel fine at rest but notice symptoms during physical activity.
- Below 40%: Reduced ejection fraction. This is the threshold for heart failure with reduced ejection fraction. The lower the number drops, the higher the risk of serious complications like cardiac arrest.
- Above 75%: This can also signal a problem, often a thickening of the heart muscle that leaves less room for blood to fill the chamber.
Doctors further classify heart failure into three categories based on these cutoffs: reduced (below 40%), mildly reduced or “mid-range” (40% to 49%), and preserved (50% or above). Heart failure with preserved ejection fraction is a condition where the heart pumps out a normal percentage of blood but is too stiff to fill properly between beats, so the total volume pumped is still inadequate.
How It’s Measured
The most common test is an echocardiogram, which uses sound waves to create a moving picture of your heart. A technician presses a small device against your chest, and the images show how much your heart walls move with each contraction. It’s painless, takes about 30 to 60 minutes, and doesn’t involve radiation.
For a more precise reading, your doctor may order a MUGA scan. This nuclear imaging test involves injecting a small amount of radioactive tracer into your bloodstream, then tracking it with a specialized camera as it passes through your heart. MUGA scans tend to give a more exact ejection fraction number than echocardiograms.
Cardiac MRI is another option and is considered the gold standard for accuracy. It produces highly detailed images of the heart muscle and can detect subtle damage that other tests might miss. It’s typically reserved for cases where the diagnosis is uncertain or when other tests give conflicting results.
What Causes a Low Ejection Fraction
A low ejection fraction means the heart muscle has been weakened or damaged. The most common culprit is coronary artery disease, where narrowed or blocked arteries starve the heart muscle of oxygen over time. A heart attack causes more sudden damage, killing a section of muscle that can no longer contract.
Other causes include faulty heart valves that force the heart to work harder, irregular heart rhythms that disrupt the heart’s pumping efficiency, and inherited or acquired diseases of the heart muscle itself. Long-standing high blood pressure, heavy alcohol use, and certain chemotherapy drugs can also weaken the heart over months or years.
Symptoms of a Low Ejection Fraction
When your heart can’t pump enough blood, the effects show up throughout your body. Shortness of breath is often the first thing people notice, especially during activities like climbing stairs or walking uphill. As the condition progresses, you may feel breathless even at rest or while lying flat, which can make sleeping difficult.
Fatigue and weakness are common because your muscles aren’t getting the oxygen-rich blood they need. Fluid starts to back up in places it shouldn’t: your ankles and lower legs swell, your abdomen may feel bloated, and you might gain weight rapidly from retained water. Other signs include a persistent cough, nausea, loss of appetite, heart palpitations, dizziness, and needing to urinate frequently, especially at night. Swollen neck veins are a visible sign that pressure is building up in the blood vessels returning blood to the heart.
The severity of symptoms generally tracks with the number. Someone with an ejection fraction of 45% might only feel winded during exercise, while someone at 25% could struggle with confusion, weakness, and breathing difficulty even while sitting still.
Can Ejection Fraction Improve?
Yes, and sometimes significantly. When the underlying cause is treatable, the heart muscle can recover a meaningful amount of pumping strength. In patients who undergo procedures to restore blood flow after coronary artery disease, ejection fraction typically improves within three months and peaks between three and six months. One study found that patients whose ejection fraction averaged about 36% before treatment saw it rise to around 46% within that window, a gain of roughly 10 percentage points. That improvement held steady through at least 12 months.
The timeline matters. Doctors now recognize that checking ejection fraction too soon after a procedure (within the first three months) may underestimate how much recovery is still ahead. The three-to-twelve-month window gives a more accurate picture of where your heart function will settle.
Not every case is reversible. If the heart muscle has been permanently scarred by a large heart attack or years of uncontrolled disease, recovery may be limited. But even modest improvements in ejection fraction can translate to noticeably better energy, less shortness of breath, and a lower risk of hospitalization.
Treatment for Reduced Ejection Fraction
Treatment depends on the severity of the drop and the cause behind it. For heart failure with reduced ejection fraction, medications form the backbone of therapy. Several drug classes work together to reduce the workload on the heart, prevent further damage, and help the muscle pump more effectively. Your doctor will typically start a combination and adjust doses over weeks to months.
For heart failure with preserved ejection fraction, where the heart pumps normally but fills poorly, treatment options have expanded recently. A class of drugs originally developed for diabetes has become a first-line recommendation after large trials showed they substantially reduce hospitalizations. Weight loss medications have also shown meaningful benefits for patients who have both obesity and preserved ejection fraction, improving symptoms, exercise capacity, and markers of heart strain.
Lifestyle changes matter at every stage. Limiting salt intake helps control fluid retention. Staying physically active within your limits strengthens the cardiovascular system. Monitoring your weight daily can catch fluid buildup early, before symptoms worsen.
When Devices Are Recommended
If ejection fraction drops below 35% and remains there despite optimal medication, doctors may recommend an implantable device. A cardiac resynchronization therapy (CRT) device is a specialized pacemaker that coordinates the timing of your heart’s contractions, helping both sides of the heart pump in sync. It’s recommended for patients whose heart’s electrical signals are delayed, which shows up as a widened pattern on an EKG.
An implantable cardioverter-defibrillator (ICD) monitors your heart rhythm continuously and delivers a shock if it detects a dangerously fast or chaotic rhythm. Because the risk of sudden cardiac arrest rises as ejection fraction falls, an ICD is often combined with CRT in the same device for patients who meet both criteria. These devices are placed under the skin near the collarbone in a procedure that typically takes one to three hours, and most people go home the next day.
The 35% threshold is important because it’s the point where the statistical risk of life-threatening rhythm problems becomes high enough that the benefits of a device clearly outweigh the risks of implantation.