Systolic dysfunction means the heart’s main pumping chamber, the left ventricle, can’t contract with enough force to push a normal amount of blood out to the body. A healthy heart ejects about 55% to 70% of the blood it holds with each beat. In systolic dysfunction, that number drops to 40% or below, a measurement called ejection fraction. This is the defining feature of what cardiologists call heart failure with reduced ejection fraction, or HFrEF.
How a Weakened Squeeze Affects Blood Flow
During each heartbeat, your left ventricle fills with blood and then contracts to send it out through the aorta. The speed and strength of that contraction determine how much blood actually leaves the chamber. In systolic dysfunction, the muscle fibers shorten more slowly and with less force. Because there’s only a brief window of time for ejection, that slower squeeze means less blood gets pushed out per beat.
The blood that doesn’t get ejected stays behind. This leftover volume raises pressure inside the ventricle, which backs up into the lungs and, eventually, into the veins throughout the body. That backup of pressure and fluid is what produces most of the symptoms people experience. Over time, the ventricle itself stretches and enlarges as it tries to compensate for its weaker contractions, a process called remodeling that can make the problem progressively worse.
Common Causes
Coronary artery disease is the single most common cause. Fatty buildup narrows the arteries that supply the heart muscle with oxygen. When blood flow drops enough to damage or kill heart tissue (a heart attack), the affected area can no longer contract normally, and overall pumping strength declines. Even without a full heart attack, years of reduced blood supply can gradually weaken the muscle.
High blood pressure forces the heart to work harder with every beat. Over years, this extra workload can cause the muscle to thicken, stiffen, and eventually weaken. Other causes include heart valve disease, viral infections that inflame the heart muscle (myocarditis, including from COVID-19), congenital heart defects, heavy alcohol use, recreational drug use, and certain chemotherapy medications. Some people inherit genetic conditions that directly weaken the heart muscle, a group of diseases called cardiomyopathies.
Symptoms to Recognize
The hallmark symptom is shortness of breath, especially during physical activity. It’s common in the general population and has many causes, which makes it a poor standalone indicator. But when shortness of breath worsens over time, appears at rest, or wakes you up at night, it becomes more telling.
A few patterns are particularly characteristic:
- Orthopnea: breathlessness that comes on when you lie flat and improves when you sit up or prop yourself on pillows.
- Paroxysmal nocturnal dyspnea: waking up suddenly at night gasping for air, typically an hour or two after falling asleep, caused by fluid shifting back toward the lungs while you’re lying down.
- Ankle and foot swelling: fluid retention from backed-up venous pressure, often worse at the end of the day.
Fatigue and reduced exercise tolerance are also extremely common. The heart simply can’t deliver enough blood to meet the body’s demand during exertion, so everyday activities like climbing stairs or carrying groceries become disproportionately tiring. Some people also develop a persistent cough or wheezing from fluid congestion in the lungs, which can be mistaken for asthma or a respiratory infection.
How It’s Diagnosed
An echocardiogram (an ultrasound of the heart) is the primary tool. It measures how much blood the left ventricle holds before and after each contraction, then calculates the ejection fraction. The formula is straightforward: the difference between the volume at full fill and the volume after contraction, divided by the volume at full fill. A result of 40% or below confirms systolic dysfunction.
The American College of Cardiology recognizes several categories based on this number. An ejection fraction of 50% or higher is considered preserved (normal pumping, with heart failure symptoms caused by stiffness rather than weakness). Between 41% and 49% is “mildly reduced.” At 40% or below, the diagnosis is heart failure with reduced ejection fraction. There’s also a newer category for people whose ejection fraction was once 40% or below but has improved to above 40% with treatment.
The echo also reveals wall motion abnormalities, meaning sections of the heart muscle that aren’t contracting properly. These are especially common after a heart attack, where the damaged area may be completely still (akinetic) or moving weakly (hypokinetic) compared to surrounding healthy muscle.
How It Differs From Diastolic Dysfunction
Systolic dysfunction is a problem with squeezing. Diastolic dysfunction is a problem with relaxing and filling. In diastolic dysfunction, the left ventricle becomes thick and stiff, so it can’t expand fully to accept blood between beats. The ejection fraction often looks normal (50% or above) because the ventricle ejects a reasonable percentage of whatever blood it holds, but the total volume is reduced because less blood got in.
In systolic dysfunction, the ventricle actually enlarges and holds more blood than normal, but it can’t push enough of it out. Both types lead to similar symptoms (shortness of breath, fatigue, swelling), but they involve different structural changes and respond to somewhat different treatments.
Treatment Approach
The core medications for systolic dysfunction work by reducing strain on the heart and, in some cases, helping the muscle recover. The standard combination includes three types of drugs: one that blocks the hormonal system driving fluid retention and blood vessel constriction (ACE inhibitors or related alternatives), one that slows the heart rate and reduces the heart’s workload (beta-blockers), and one that blocks a hormone called aldosterone that promotes scarring and fluid buildup in the heart. Diuretics (water pills) are added to relieve fluid congestion when swelling or breathlessness is present.
These medications don’t just manage symptoms. They reduce hospitalization rates and extend survival. Treatment is typically started at low doses and gradually increased as tolerated, a process that can take weeks to months.
For people whose ejection fraction drops to 35% or below, the risk of dangerous heart rhythm problems rises significantly. At that threshold, an implantable defibrillator may be recommended to detect and correct life-threatening rhythms automatically. Some patients also benefit from a specialized pacemaker (cardiac resynchronization therapy) that coordinates the timing of the left and right ventricles to improve pumping efficiency.
Lifestyle Changes That Matter
Sodium restriction is one of the most consistent recommendations across international guidelines. Most guidelines advise keeping salt intake below about 5 to 6 grams per day (roughly one teaspoon). Interestingly, moderate restriction appears to work better than very strict limitation. Cutting below about 3.75 grams of salt daily hasn’t shown clear additional benefit and may cause problems of its own.
Regular exercise is recommended by every major heart failure guideline. Cardiac rehabilitation programs improve exercise tolerance, physical function, and quality of life. This may seem counterintuitive when the heart is weak, but supervised, gradual exercise helps the body use oxygen more efficiently and can partially offset the heart’s reduced output. Fluid restriction (typically 1.5 to 2 liters per day) is generally reserved for advanced cases with significant fluid retention.
Long-Term Outlook
Systolic dysfunction is a serious condition with significant mortality risk. Data from large registries show that five-year mortality for people hospitalized with heart failure is roughly 75%, regardless of whether ejection fraction is reduced or preserved. In outpatient settings, the picture is somewhat better: one-year mortality for people with reduced ejection fraction is around 8.8%, compared to 6.3% for those with preserved ejection fraction.
These numbers reflect averages across large populations, and individual outcomes vary widely depending on the underlying cause, how early treatment begins, and how well someone responds to medication. The existence of an “improved ejection fraction” category in current guidelines reflects a real phenomenon: with optimal treatment, some people see their ejection fraction climb back above 40%, sometimes substantially. That recovery is associated with a meaningfully better prognosis, which is one reason aggressive early treatment matters so much.