Heart failure with reduced ejection fraction (HFrEF) means your heart’s main pumping chamber, the left ventricle, can no longer squeeze out enough blood with each beat. Specifically, it’s defined as an ejection fraction of 40% or below. A healthy heart typically ejects 55% to 70% of the blood in the left ventricle with each contraction, so falling to 40% or less represents a significant drop in pumping power. This doesn’t mean your heart has stopped working; it means it’s working inefficiently, and the rest of your body may not be getting the oxygen-rich blood it needs.
What Ejection Fraction Actually Measures
Ejection fraction is a percentage. It tells you how much of the blood sitting in the left ventricle gets pushed out during each heartbeat. If your ventricle holds 100 mL of blood and pumps out 60 mL, your ejection fraction is 60%, which is normal. In HFrEF, that number drops to 40% or below, meaning more blood stays behind in the chamber after each beat.
Current guidelines from the American Heart Association and American College of Cardiology also recognize two other categories. Heart failure with mildly reduced ejection fraction (HFmrEF) falls in the 41% to 49% range, and heart failure with preserved ejection fraction (HFpEF) applies when the number is 50% or higher but the heart still isn’t filling or relaxing properly. The distinction matters because treatment strategies differ across these groups, and HFrEF has the strongest evidence base for specific medications.
If someone with HFrEF improves their ejection fraction above 40% with treatment, they’re reclassified as having “heart failure with improved ejection fraction.” Even so, guidelines recommend continuing the same medications, because stopping them often leads to a decline back to the reduced range.
What Causes the Heart to Weaken
The single most common cause worldwide is ischemic heart disease, meaning reduced blood flow to the heart muscle itself. A heart attack kills a section of muscle tissue, and that dead zone can no longer contract. Over time, the remaining muscle may not compensate well enough, and overall pumping strength falls. Chronic coronary artery disease can do the same thing more gradually, starving the muscle of oxygen without a dramatic event.
Beyond blocked arteries, a long list of non-ischemic causes can lead to HFrEF:
- Dilated cardiomyopathy: the heart chamber stretches and thins, often without a clear cause or due to genetic factors
- Viral infections that inflame the heart muscle (myocarditis)
- Long-standing high blood pressure, which forces the heart to work harder for years
- Valvular heart disease, where leaky or narrowed valves create extra workload
- Substance use, particularly heavy alcohol, cocaine, or methamphetamine use
- Certain chemotherapy drugs that are toxic to heart cells
- Thyroid disorders, diabetes, and obesity
- Peripartum cardiomyopathy, a form that develops late in pregnancy or shortly after delivery
- Infiltrative diseases like cardiac amyloidosis, sarcoidosis, or hemochromatosis, where abnormal substances deposit in heart tissue
In about a third of cases, no clear cause is ever identified, and the condition is labeled idiopathic dilated cardiomyopathy.
What Happens Inside the Heart Muscle
HFrEF isn’t just a weak squeeze. The heart undergoes extensive remodeling at the cellular level. The contractile proteins inside heart muscle cells, the tiny fibers that actually generate force, become disorganized and eventually break down. A structural protein called titin, which acts like a molecular spring helping the heart fill and contract, decreases significantly. The cells try to compensate by beefing up their internal scaffolding, but this stiffens the muscle without improving its ability to pump.
At the same time, heart cells begin to die. The primary mode of cell death is a self-digesting process called autophagy, where damaged cells essentially consume themselves. Acute oxygen deprivation kills additional cells. As cells die, the body replaces them with scar tissue (fibrosis), which cannot contract. The communication channels between neighboring heart cells, called gap junctions, also deteriorate, disrupting the electrical signals that coordinate each heartbeat.
The result is a heart that is stiffer, less coordinated, and weaker, with three overlapping problems: loss of contractile fibers, buildup of rigid structural proteins, and progressive scarring. This is why HFrEF tends to worsen over time without treatment. The remodeling feeds on itself.
How It Feels Day to Day
Symptoms depend on how far the condition has progressed. Doctors use a four-tier classification system from the New York Heart Association to describe functional limitations:
- Class I: No symptoms during ordinary activity. You might not know anything is wrong without testing.
- Class II: Comfortable at rest, but everyday activities like climbing stairs or carrying groceries cause fatigue, shortness of breath, or a racing heartbeat.
- Class III: Even light activity, less than your normal routine, triggers breathlessness or exhaustion. You’re comfortable only at rest.
- Class IV: Symptoms are present even while sitting or lying down. Any physical effort makes them worse.
The hallmark symptoms are shortness of breath (especially when lying flat or waking you up at night), persistent fatigue, and swelling in the ankles, legs, or abdomen from fluid buildup. Many people also notice a dry cough, reduced appetite, or difficulty concentrating. The shortness of breath that hits when you lie down happens because fluid redistributes toward your lungs in that position. Propping yourself up on extra pillows or sleeping in a recliner often helps, and this is a classic early clue that something is off with the heart’s pumping ability.
How It’s Diagnosed
An echocardiogram, which is an ultrasound of the heart, is the standard test for measuring ejection fraction. It’s painless, takes about 30 to 45 minutes, and gives your doctor a real-time look at how your heart chambers are moving. Other imaging options include cardiac MRI, which provides more detailed pictures, and nuclear stress tests that assess blood flow during exercise.
Blood tests for a hormone called BNP or NT-proBNP help confirm the diagnosis. When the heart is under strain, it releases these proteins in higher amounts. Elevated levels support a heart failure diagnosis, while normal levels make it much less likely. Your doctor will also look at kidney function, thyroid levels, and other bloodwork to identify contributing causes.
The Four Pillars of Treatment
Modern treatment for HFrEF rests on four classes of medication that, used together, have been shown to reduce both the risk of death and hospitalization. The 2021 European Society of Cardiology guidelines and subsequent American guidelines both endorse this “four-pillar” approach:
- RAAS inhibitors (specifically a combination drug called sacubitril/valsartan, or older ACE inhibitors if that’s not tolerated): these relax blood vessels and reduce the hormonal signals that drive harmful remodeling
- Beta blockers: slow the heart rate and lower blood pressure, giving the heart more time to fill and reducing its workload
- Mineralocorticoid receptor antagonists (MRAs): block a hormone called aldosterone that promotes fluid retention and scarring in the heart
- SGLT2 inhibitors: originally developed for diabetes, these drugs reduce fluid overload and have proven benefits for heart failure regardless of whether someone has diabetes
The goal is to get all four classes on board as quickly as safely possible, since each one works through a different mechanism and the benefits stack. In practice, doses are started low and increased over weeks to months. Many patients also take a diuretic (a “water pill”) to manage fluid retention, though diuretics treat symptoms rather than slowing the disease itself.
Devices and Procedures
When medications alone aren’t enough, implantable devices can help. An implantable cardioverter-defibrillator (ICD) monitors heart rhythm and delivers a shock if a dangerous arrhythmia occurs, which is a leading cause of sudden death in people with low ejection fractions. A cardiac resynchronization therapy (CRT) device is a specialized pacemaker that coordinates the timing of the left and right ventricles, improving pumping efficiency. Some patients receive a combination device that does both.
For the most advanced cases, options include a left ventricular assist device (LVAD), a mechanical pump implanted in the chest that helps the weakened ventricle push blood forward. This can serve as a bridge while waiting for a heart transplant or as a long-term therapy for people who aren’t transplant candidates.
Outlook With Modern Treatment
HFrEF is a serious condition, but outcomes have improved substantially over the past two decades as new medications have been added to the treatment toolkit. In a large study of nearly 4,900 patients followed for five years, the mortality rate for HFrEF was about 25%, compared to roughly 18% for mildly reduced ejection fraction and 13% for preserved ejection fraction. Those numbers reflect a mixed population where not everyone received optimal therapy. In that study, only about 56% of HFrEF patients were discharged on a key class of heart failure medication, suggesting that real-world undertreatment remains a significant problem.
Patients who receive all four pillars of guideline-directed therapy and tolerate target doses generally do better than these averages suggest. Ejection fraction can improve meaningfully with treatment, sometimes climbing 10 to 15 percentage points or more. Lifestyle factors also play a real role: limiting sodium intake, staying physically active within your comfort zone, monitoring daily weight to catch fluid retention early, and avoiding alcohol all support better outcomes over time.