Low ejection fraction means your heart isn’t pumping out enough blood with each beat. A normal ejection fraction is roughly 55% or higher, meaning the heart pushes out more than half the blood in its main pumping chamber every time it contracts. An ejection fraction of 40% or below is classified as “reduced,” and the lower it drops, the higher the risk of serious complications like cardiac arrest. Several conditions can cause this, ranging from heart attacks and chronic high blood pressure to infections, alcohol use, and genetic disorders.
How Ejection Fraction Is Classified
The 2022 guidelines from the American Heart Association break heart failure into categories based on ejection fraction. An EF of 50% or above is considered preserved. An EF between 41% and 49% is mildly reduced. An EF at or below 40% is reduced, the category that carries the most concern. There’s also a newer category, “improved EF,” for people whose number was once at or below 40% but has since climbed above it with treatment.
These numbers come from imaging tests, most commonly an echocardiogram, which uses ultrasound to watch the heart contract in real time. Cardiac MRI can also measure EF and tends to be more precise, though it’s used less often as a first step.
Coronary Artery Disease and Heart Attacks
The single most common reason for a low ejection fraction is damage from blocked coronary arteries. When a heart attack cuts off blood flow to part of the heart muscle, those cells die. Dead heart muscle can’t contract, so the remaining healthy tissue has to pick up the slack. Over time, this extra workload triggers a process called remodeling: the heart chamber stretches and enlarges, its walls thin out, and the overall pumping strength declines further.
Even without a full heart attack, chronic narrowing of the coronary arteries can starve the heart of oxygen gradually. This ongoing ischemia weakens the muscle bit by bit, sometimes without dramatic symptoms. A person with no prior heart attack history can still develop a low EF from years of reduced blood flow. This is why coronary artery disease is often called the leading cause of heart failure with reduced ejection fraction.
Chronic High Blood Pressure
Long-term high blood pressure forces the heart to pump against greater resistance with every beat. The left ventricle responds by thickening its walls, similar to how a muscle grows from lifting heavy weights. But unlike a bicep, a thicker heart wall eventually becomes stiff rather than stronger. Blood pressure inside the heart rises, and the chamber can’t fill or pump as efficiently.
This process can take years or even decades to reach the point where ejection fraction drops noticeably. Many people live with thickened heart walls and no symptoms for a long time. The tipping point often comes when a second event, like a heart attack or an arrhythmia, pushes the already-strained heart into outright failure. That combination of chronic strain plus an acute trigger is a common pathway to a low EF diagnosis.
Dilated Cardiomyopathy
Dilated cardiomyopathy is a condition where the heart’s main pumping chamber stretches out and weakens without coronary artery disease being the primary driver. It has several distinct causes.
Viral Infections
Certain viruses can infect heart muscle cells directly and trigger inflammation, a condition called myocarditis. One of the best-studied culprits is coxsackievirus B, a common enterovirus. Research has found that about a third of patients with unexplained dilated cardiomyopathy had evidence of enterovirus B in their heart tissue. The virus damages heart cells by breaking down structural proteins that hold cell membranes together. In some cases, fragments of the viral genetic material persist in heart tissue long after the initial infection resolves, continuing to cause harm even without producing new infectious virus. Adenovirus and cytomegalovirus have also been linked to the condition.
Genetic Factors
Dilated cardiomyopathy runs in families in roughly 20% to 35% of cases. Mutations affecting the structural proteins of heart muscle cells can make the chamber walls prone to stretching and weakening over time. If you’ve been diagnosed with a low EF and have a close relative with heart failure, genetic testing may help clarify the cause and guide screening for other family members.
Alcohol and Substance Use
Heavy, sustained alcohol consumption is a well-recognized cause of cardiomyopathy. Drinking roughly 80 grams of alcohol per day (about five to six standard drinks) for five years or more greatly increases the risk. Alcohol-induced cardiomyopathy occurs in about 1% to 2% of people who consistently exceed recommended limits, which are generally defined as more than seven drinks per week for women and more than 14 for men.
Alcohol is directly toxic to heart muscle cells. Over years of heavy use, it weakens the heart walls, enlarges the chambers, and progressively lowers the ejection fraction. The good news is that this form of cardiomyopathy can partially or fully reverse if drinking stops early enough. Cocaine and other stimulant drugs also damage the heart, raising the risk of both heart attacks and direct muscle injury. These substances can accelerate decline in someone whose heart is already compromised.
Chemotherapy and Other Medications
Certain cancer treatments are known to be toxic to the heart. Some chemotherapy drugs, particularly a class used to treat breast cancer, lymphomas, and leukemias, can weaken heart muscle cells and reduce ejection fraction. The effect is dose-dependent: the more total drug a patient receives over their treatment course, the higher the risk. Oncologists routinely monitor ejection fraction with echocardiograms during and after treatment for this reason.
A handful of other prescription medications can contribute to reduced heart function as a side effect, though this is far less common than the causes above.
Heart Valve Disease
When a heart valve leaks significantly or doesn’t open fully, the heart has to work harder to move the same amount of blood. A leaky mitral valve, for example, allows blood to flow backward with each contraction, meaning the ventricle has to pump a larger volume to deliver the same net output to the body. Over months and years, this volume overload stretches the chamber and erodes pumping strength. Severe aortic stenosis, where the valve narrows and resists outflow, creates a pressure overload that has a similar long-term effect.
Arrhythmias
Prolonged abnormal heart rhythms can themselves cause a low ejection fraction. When the heart beats too fast for too long, as in uncontrolled atrial fibrillation or persistent tachycardia, the muscle essentially becomes exhausted. This is sometimes called tachycardia-induced cardiomyopathy, and it’s one of the more reversible causes. Restoring a normal heart rate, whether through medication or a procedure, can allow the ejection fraction to recover significantly over weeks to months.
What Low Ejection Fraction Feels Like
Symptoms tend to worsen as the number drops. Common signs include fatigue and weakness that limit everyday activities, shortness of breath during exertion or while lying flat, and swelling in the feet, ankles, or abdomen from fluid retention. Some people notice heart palpitations, dizziness, nausea, or confusion. In more severe cases, episodes of near-fainting or loss of consciousness can occur.
These symptoms develop because the heart can’t deliver enough oxygen-rich blood to meet the body’s demands. Fluid backs up into the lungs and tissues when the heart can’t pump it forward efficiently. The body compensates by retaining extra salt and water, which adds to the swelling and congestion. The heart itself tries to compensate by beating faster and enlarging further, but these adaptations eventually create more scar tissue and stiffness, driving the EF even lower in a self-reinforcing cycle.
Can Ejection Fraction Improve?
It depends entirely on the cause. Some forms of low EF are at least partially reversible. Alcohol-related cardiomyopathy can improve substantially with abstinence. Tachycardia-induced cardiomyopathy often recovers once heart rate is controlled. Viral myocarditis sometimes resolves on its own or with treatment, particularly if caught early. Even in cases caused by a heart attack, modern medications and devices can help the heart remodel in a healthier direction, and the 2022 guidelines specifically recognize “improved EF” as its own category because many patients do see meaningful gains.
On the other hand, extensive scarring from a large heart attack or advanced genetic cardiomyopathy may limit how much recovery is possible. The trajectory varies widely from person to person, which is why identifying the underlying cause matters so much. Treating high blood pressure, fixing a damaged valve, stopping alcohol use, or managing an arrhythmia doesn’t just address the symptom. It targets the specific mechanism driving the heart’s decline.