A heart function of 45% means your heart is pumping out 45% of the blood in its main chamber with each beat. This number, called ejection fraction, falls below the normal range of 55% to 70%. At 45%, your heart function is considered borderline low, sitting in a category doctors call “mildly reduced.” It’s not normal, but it’s not severely impaired either.
What Ejection Fraction Actually Measures
Your heart’s left ventricle fills with blood between beats, then squeezes to push that blood out to the rest of your body. Ejection fraction is simply the percentage of blood that gets pushed out with each squeeze. If the chamber holds 100 milliliters and pumps out 45 milliliters, your ejection fraction is 45%.
The ranges break down like this:
- Normal: 55% to 70%
- Borderline low (mildly reduced): 40% to 49%
- Below 40%: The heart is struggling to supply enough blood to the body
At 45%, you’re 10 percentage points below the low end of normal. Your heart is still moving blood, but it’s working less efficiently than it should be. Cardiologists classify this as heart failure with mildly reduced ejection fraction, sometimes abbreviated HFmrEF. The word “failure” sounds alarming, but it doesn’t mean your heart has stopped working. It means the heart isn’t pumping as strongly as a healthy heart would.
How Accurate Is the Number
Most people get their ejection fraction measured by a standard echocardiogram, which uses ultrasound to watch the heart in real time. This is fast, widely available, and completely painless. But it’s not perfectly precise. Standard 2D echocardiograms can vary by as much as 10 percentage points compared to cardiac MRI, which is considered the gold standard. That means a reading of 45% on an echo could represent a true value anywhere from roughly 35% to 55%.
Three-dimensional echocardiography is more accurate, with variations closer to 6%. Cardiac MRI is the most reproducible, with repeat measurements typically varying by less than 5%. If your 45% reading came from a standard echo and your doctor is making important treatment decisions based on it, they may order a follow-up test or a cardiac MRI to confirm the number. A few percentage points in either direction can change which category you fall into and which treatments are recommended.
What Causes the Heart to Weaken
A mildly reduced ejection fraction doesn’t happen on its own. Something is making the heart muscle pump less effectively. The most common culprits include high blood pressure, coronary artery disease (narrowed or blocked arteries supplying the heart), and heart valve problems. Long-standing high blood pressure forces the heart to work harder over time, eventually thickening and stiffening the muscle in ways that reduce its pumping ability.
Other causes include a previous heart attack, which can scar the heart muscle permanently, irregular heart rhythms like atrial fibrillation, viral infections that inflame the heart, diabetes, obesity, and chronic kidney disease. In some cases, the cause is genetic. Your doctor will typically run additional tests to figure out what’s driving your specific situation, because treating the underlying cause is often the most effective way to protect or improve your heart function.
Symptoms You Might Notice
Some people with a 45% ejection fraction feel completely fine, especially if the decline happened gradually and their body has compensated. Others notice symptoms that creep in over weeks or months. The most common is shortness of breath, particularly during physical activity or when lying flat. You might find that you need an extra pillow at night, or that climbing stairs leaves you more winded than it used to.
Fatigue is another hallmark. When the heart pumps less blood per beat, your muscles and organs get less oxygen, and everyday tasks can feel more draining. Some people notice swelling in their ankles, feet, or legs as fluid backs up in the body. Others experience a persistent cough, difficulty concentrating, or a rapid or irregular heartbeat. None of these symptoms are unique to heart failure, which is part of why the condition often goes undiagnosed until an imaging test reveals the reduced ejection fraction.
How 45% Is Treated
Treatment at this level focuses on two goals: preventing further decline and, when possible, improving the number. The American Heart Association’s 2022 guidelines recommend a class of medications called SGLT2 inhibitors as a first-line option for mildly reduced ejection fraction. These drugs, originally developed for diabetes, have shown clear benefits for heart failure patients regardless of whether they have diabetes.
Several other medication classes may also be used, including ACE inhibitors, ARBs, mineralocorticoid receptor antagonists, and beta blockers, though the evidence supporting these in the mildly reduced range is less robust than for people with ejection fractions below 40%. Your cardiologist will tailor the medication plan based on your specific symptoms, underlying cause, and how you respond to treatment.
Beyond medications, managing the root cause matters enormously. If high blood pressure is the driver, getting it under control can halt or reverse the damage. If coronary artery disease is involved, procedures to restore blood flow or medications to reduce the heart’s workload can help. For people with atrial fibrillation, restoring a normal rhythm may improve ejection fraction on its own.
Can Ejection Fraction Improve
Yes, and 45% is a range where improvement is genuinely possible. How much depends on the cause, how long the heart has been weakened, and how aggressively the underlying problem is treated. People whose ejection fraction dropped due to a reversible cause, like uncontrolled blood pressure or a viral infection, often see meaningful recovery.
Lifestyle changes can make a real difference. An epidemiological review found that people who maintained regular exercise, healthy eating habits, and a normal BMI had up to 81% lower rates of developing heart failure in the first place. For people who already have reduced function, dietary changes have shown striking results in small studies. In one case, a patient with an ejection fraction of 35% followed a whole-food plant-based diet for 60 days and saw their ejection fraction normalize to 50%. A series of three heart failure patients on similar diets for an average of 79 days showed a 92% improvement in ejection fraction along with significant improvements in heart structure.
These are small studies and individual cases, not large clinical trials, so the results won’t apply to everyone. But they illustrate that the heart muscle can recover function under the right conditions, especially when the damage isn’t from permanent scarring. Regular moderate exercise, sodium restriction, maintaining a healthy weight, and limiting alcohol are all consistently recommended for people in this range.
Long-Term Outlook
The prognosis for a mildly reduced ejection fraction is generally better than for people with more severe reductions, at least in the short term. Research shows that all-cause mortality risk is lower for people in the 40% to 49% range compared to those below 40% at one, two, and three years. Beyond three years, that gap tends to narrow, possibly because ejection fraction can shift over time in either direction.
That shifting nature is actually one of the defining features of this category. Some people with a 45% ejection fraction will improve to normal with treatment. Others will remain stable for years. A smaller number will see further decline, particularly if the underlying cause isn’t well controlled. Regular monitoring, typically with repeat echocardiograms every 6 to 12 months, helps track which direction things are heading and allows your treatment plan to be adjusted accordingly.