The Most Misunderstood Heart Number (Plus Your Tune-Up Checklist)

Updated July 2026

One of the most important numbers in cardiology is also one of the most misunderstood. It is your ejection fraction, or EF, and patients often read it the wrong way and frighten themselves over nothing. Let me pull back the curtain on what it really measures.

What is ejection fraction?

Ejection fraction is the percentage of blood your heart pushes out with each beat. Your heart has four chambers, but the heavy lifter is the left ventricle, the muscular chamber that pumps oxygen-rich blood to your whole body. When we talk about how well your heart is squeezing, we are almost always talking about the left ventricle.

We measure it with an echocardiogram, which is simply an ultrasound of the heart. About 10 million of these are done in the US every year. A cardiac MRI can measure EF too, but the echo is the usual tool. Listening with a stethoscope, or checking your EKG for the record, cannot tell us your EF. And checking it is not a routine part of a physical. Something has to prompt it, like an abnormal EKG, a heart murmur, or a symptom that could be coming from the heart, such as new shortness of breath, palpitations, or unusual fatigue.

What is a normal ejection fraction?

A normal ejection fraction sits between 50 and 70 percent, not at 100. This is where the misunderstanding starts. Someone sees a result of 55 percent and worries they have lost the other 45. That is not how the heart works. A healthy heart never empties completely. It only pushes out a portion of what it holds with each beat, and squeezing out half to two-thirds is exactly right. Mayo Clinic uses the same range.

Here is how we categorize the numbers:

• 50 to 70 percent: normal.
• 40 to 49 percent: mildly reduced.
• 30 to 39 percent: moderately reduced.
• Below 30 percent: markedly reduced.

So an EF of 45 percent does not mean you are running at half capacity. You are only about 5 percent below the normal range. Abnormal, yes, but only slightly.

Why does ejection fraction drop?

EF usually falls when the heart muscle becomes damaged or scarred. The most frequent cause is a heart attack, which leaves behind permanent muscle damage. Certain viral infections can inflame the heart muscle, a condition called myocarditis. Severe valve disease can overwork the muscle until it weakens. Some chemotherapy drugs are toxic to the heart, which is why cancer patients often need regular echocardiograms. In rare cases EF can drop during or after pregnancy, known as peripartum cardiomyopathy. And regular heavy drinking can lower EF, because alcohol is toxic to heart muscle, which is one more good reason to keep your intake modest.

Can a low ejection fraction be fixed?

Sometimes. When the cause is alcohol, a viral infection, or a valve problem, the heart can often recover once the underlying issue is treated. Damage from a heart attack, the most common cause of a low EF, is usually permanent. That is why avoiding a heart attack in the first place is your best insurance against reduced heart function. As with everything involving the heart, the best offense is a good defense.

But here's the genuinely reassuring part, and it's a message I want every patient with a low number to hear: a reduced ejection fraction is one of the most treatable conditions in all of cardiology. Even when the underlying muscle damage is permanent, modern heart failure medications, often described as the "four pillars" of treatment, can dramatically improve symptoms, keep people out of the hospital, extend life, and in many cases actually raise the EF back up over time. A low EF today is not a fixed sentence. It's the starting point for treatment that works remarkably well.

How do you keep your ejection fraction healthy?

Protect the heart muscle before anything gets the chance to damage it. Your heart is built to last 100 years or more, but it is not a set-it-and-forget-it machine. To keep your left ventricle pumping in that 50 to 70 percent range:

• Move daily. Regular exercise keeps the muscle strong.
• Watch the fuel. Eat for health rather than for disease, which is exactly what Step One Foods is built to make easy.
• Check your stats. High blood pressure, cholesterol, and blood sugar are silent stressors on your heart's arteries, and they can trigger a heart attack out of the blue. Bring them into range with lifestyle first, and medication if you need it.
• If you smoke, quit. This remains the single best thing you can do for your blood vessels.

Can your ejection fraction be normal and your heart still be in trouble?

Yes, and this trips people up. It's natural to assume a normal EF means the heart is completely fine, but that isn't always so. About half of all heart failure occurs in people whose ejection fraction is actually normal, a condition called heart failure with preserved ejection fraction. In these cases the heart squeezes well but has become stiff and doesn't relax and fill properly between beats, so symptoms like shortness of breath and swelling can appear despite a reassuring EF number. It's yet another reason the EF is just one piece of the picture, best interpreted by your physician alongside your symptoms and the rest of your evaluation, not read in isolation.

The bottom line

A number like 55 percent is not a grade you failed by 45 points. It is a healthy heart doing exactly what it should. Think of a heart tune-up as something you schedule regularly, not something you wait for symptoms to force on you. If it has been a while since anyone checked your heart vitals, now is a good time to get going.

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