LVEF stands for left ventricular ejection fraction, and it measures how well your heart pumps blood with each beat. Expressed as a percentage, it tells you how much of the blood sitting in your heart’s main pumping chamber (the left ventricle) actually gets pushed out to the rest of your body each time the heart contracts. A normal LVEF is 50% or higher, meaning at least half of the blood in the chamber is ejected with every heartbeat.
How LVEF Is Calculated
Your left ventricle fills with blood between heartbeats, then squeezes to push that blood into your aorta and out to your body. LVEF captures the efficiency of that squeeze. The formula is straightforward: take the amount of blood pumped out (called stroke volume), divide it by the total amount of blood in the ventricle just before it contracts, and multiply by 100 to get a percentage.
So if your left ventricle holds 100 mL of blood before contracting and pumps out 60 mL, your LVEF is 60%. That remaining 40 mL stays behind and mixes with fresh blood flowing in for the next beat. Even a perfectly healthy heart never empties completely.
What the Numbers Mean
The 2022 guidelines from the American Heart Association, American College of Cardiology, and Heart Failure Society of America break LVEF into three categories when heart failure is present:
- 50% or higher: Preserved ejection fraction. The heart squeezes normally, though heart failure can still occur if the ventricle becomes stiff and doesn’t fill properly.
- 41% to 49%: Mildly reduced ejection fraction. The heart’s pumping ability is below normal but not severely impaired.
- 40% or below: Reduced ejection fraction. This is the threshold that defines the most studied form of heart failure and triggers specific treatment decisions.
Research tracking cardiovascular outcomes has identified key inflection points in risk. Cardiovascular death risk rises meaningfully once LVEF drops below 50%. The risk of being hospitalized for heart failure climbs more steeply below 40%, and the risk of dying specifically from the heart’s inability to pump (pump failure) increases below 40% as well. An LVEF of 35% is another important threshold, often used to determine whether someone qualifies for an implantable defibrillator.
How LVEF Is Measured
The most common way to measure LVEF is with an echocardiogram, an ultrasound of the heart. It’s noninvasive, widely available, and relatively inexpensive. A technician places a probe on your chest, and the sound waves create a moving image of your heart that allows measurement of chamber sizes and pumping function. The test typically takes 30 to 60 minutes.
Cardiac MRI is considered the gold standard for accuracy because it produces highly detailed images of the heart’s structure and volume. Three-dimensional echocardiography comes closer to cardiac MRI’s precision than traditional two-dimensional echo, making it a preferred first-line option in situations where accuracy is especially critical, such as monitoring heart damage from chemotherapy. In practice, most people get a standard echocardiogram first, and cardiac MRI is reserved for cases where more precise measurement is needed or echo images are unclear.
What Causes a Low LVEF
Coronary artery disease is the single most common cause of reduced ejection fraction. When one or more arteries supplying the heart muscle become blocked or narrowed, parts of the heart wall can weaken or die (as in a heart attack), leaving the ventricle unable to contract as forcefully.
Other common causes include high blood pressure that has gone untreated for years, diseases of the heart valves, and dilated cardiomyopathy, a condition where the heart muscle stretches and thins. Viral infections can inflame the heart muscle directly, sometimes causing a sudden drop in LVEF. Certain chemotherapy drugs are known to damage heart cells. Long-term heavy use of alcohol, cocaine, or methamphetamines can weaken the heart as well. Less common causes include thyroid disorders, autoimmune diseases, genetic heart conditions, and abnormal heart rhythms that persist long enough to tire out the muscle.
Some causes are reversible. Stress cardiomyopathy (sometimes called broken heart syndrome) can temporarily drop LVEF to dangeringly low levels, but the heart often recovers fully within weeks. Peripartum cardiomyopathy, which develops late in pregnancy or shortly after delivery, also has a meaningful recovery rate with treatment.
Symptoms of Low Ejection Fraction
When LVEF drops low enough that the heart can’t meet the body’s demand for blood, symptoms of heart failure develop. These can come on gradually or appear suddenly. The most recognizable ones include shortness of breath during activity or while lying flat, persistent fatigue and weakness, and swelling in the legs, ankles, and feet caused by fluid backing up in the body. A rapid or irregular heartbeat is also common as the heart tries to compensate for its weakened pumping.
Some people with a mildly reduced LVEF feel perfectly fine at rest and only notice symptoms during exercise or exertion. Others, particularly those with LVEF below 30%, may feel breathless with minimal activity or even at rest. The severity of symptoms doesn’t always match the number on the echo report, though. Some people with an LVEF of 25% function surprisingly well, while others with an LVEF of 45% feel significantly limited.
Can LVEF Improve?
Yes, and this is one of the more encouraging aspects of modern heart failure treatment. Current guidelines recommend a combination of four medication classes for people with reduced ejection fraction: a drug that combines a neprilysin inhibitor with a blood pressure blocker (sacubitril-valsartan), a specific type of beta-blocker, a mineralocorticoid antagonist, and an SGLT-2 inhibitor (a class originally developed for diabetes but now proven to help heart failure regardless of diabetes status). Together, these medications reduce the heart’s workload, slow harmful remodeling of the heart muscle, and reduce fluid buildup.
This combination has been shown to reduce both death and hospitalization. A study of young adults with acute heart failure found that those whose LVEF improved within a year had a mortality rate of 9.4%, compared to 32.8% for those whose LVEF did not recover. That threefold difference underscores how much recovery matters. The greatest benefit appeared when LVEF improved by 30 to 40 percentage points from its lowest value.
One important principle in current guidelines: if your LVEF improves above 40% with treatment, you should continue taking your medications. Stopping them risks a relapse, with the heart weakening again even if you feel fine. The improvement reflects what the medications are doing for your heart, not a permanent cure that allows you to stop therapy.
LVEF With Preserved Ejection Fraction
An LVEF of 50% or above doesn’t guarantee a healthy heart. In heart failure with preserved ejection fraction, the heart squeezes normally but has become stiff, making it harder to fill with blood between beats. The result is the same pool of symptoms: shortness of breath, fatigue, and fluid retention. This type of heart failure is more common in older adults and people with obesity, high blood pressure, or diabetes. It has historically been harder to treat than reduced ejection fraction, though SGLT-2 inhibitors have recently shown benefits in this group as well.