Heart failure is a condition where your heart can’t pump blood efficiently enough to meet your body’s needs. It doesn’t mean your heart has stopped working. It means the heart muscle has become too weak, too stiff, or too damaged to keep up with demand, leading to a buildup of fluid and a shortage of oxygen-rich blood reaching your organs and tissues. About half of people with heart failure have a heart that can’t squeeze forcefully enough, while the other half have a heart that can’t relax and fill properly between beats.
How Heart Failure Works
Your heart is a pump. With every beat, it fills with blood, then contracts to push that blood out to your lungs and body. Heart failure disrupts one or both sides of this cycle.
In one form, the heart muscle weakens and the chambers stretch out. The walls become thinner and the heart dilates, losing its ability to contract with enough force. This often happens after a heart attack destroys a section of muscle, or after years of damage from valve disease, infection, or inherited conditions. Doctors call this “reduced ejection fraction” because the percentage of blood pumped out with each beat drops below normal.
In the other form, the heart muscle thickens and stiffens. It can still squeeze, but it can’t relax enough to fill properly between beats. Less blood enters the chambers, so less blood gets pumped out. This is called “preserved ejection fraction” and is more commonly driven by high blood pressure, obesity, and diabetes. It tends to affect older adults and women more often.
The distinction matters because these two types respond differently to treatment. Most medications proven to extend life in heart failure work for the reduced-ejection-fraction type. Treatment options for the preserved type are more limited, though newer drug classes are beginning to show benefit.
Common Causes
Coronary artery disease and heart attacks are the leading causes of the weakened-pump form. When blood flow to part of the heart is blocked, that section of muscle dies and can’t contribute to pumping. Faulty heart valves, irregular heart rhythms, and inherited heart muscle diseases also cause this type.
High blood pressure is the primary driver of the stiff-heart form. Years of pumping against elevated pressure forces the heart muscle to thicken, and eventually it loses its flexibility. Obesity and diabetes compound the problem by promoting inflammation and fibrosis in the heart tissue, making the walls even stiffer. In many cases, several of these conditions overlap, accelerating the damage.
Symptoms to Recognize
Shortness of breath is usually the first thing people notice, especially during activities that didn’t used to be difficult, like climbing stairs or carrying groceries. As the condition progresses, even light activity can leave you winded.
Fluid buildup produces its own set of warning signs. When the heart falls behind, blood backs up in the veins, and fluid leaks into tissues. You may notice swelling in your ankles, lower legs, or abdomen. Shoes that suddenly feel tight or unexplained weight gain over a few days are common clues. Some people develop visible swelling in the neck veins.
Difficulty sleeping flat is another hallmark. Lying down allows fluid to redistribute toward the lungs, making it harder to breathe. Many people with heart failure learn to prop themselves up on pillows or sleep in a recliner. Persistent fatigue, even after rest, rounds out the picture, because your muscles and organs aren’t getting the oxygen-rich blood they need.
How It’s Classified
Heart failure is categorized two ways: by how much pumping power the heart has lost, and by how far the disease has progressed.
By Ejection Fraction
Ejection fraction (EF) measures the percentage of blood pumped out of the main chamber with each beat. A normal EF is roughly 55% to 70%. Heart failure classifications break down like this:
- Reduced EF (HFrEF): 40% or below. The heart is too weak to contract effectively.
- Mildly reduced EF (HFmrEF): 41% to 49%. A borderline zone where the heart is underperforming but not severely weakened.
- Preserved EF (HFpEF): 50% or above. The heart squeezes normally but can’t relax and fill properly.
- Improved EF (HFimpEF): Started at 40% or below but has improved by at least 10 points with treatment, rising above 40%. This is a newer category recognizing that some hearts recover significant function.
By Disease Stage
The American College of Cardiology uses four stages that track how far heart failure has advanced. These stages only move forward; you can’t go back to an earlier stage.
- Stage A (At risk): No heart damage yet, but risk factors like high blood pressure, diabetes, or obesity put you on the path. Intervention at this point focuses entirely on controlling those risk factors.
- Stage B (Pre-heart failure): Structural changes are detectable, such as thickened walls or a slightly enlarged chamber, but you have no symptoms yet.
- Stage C (Symptomatic): Structural changes plus current or past symptoms of heart failure. This is when most people receive their diagnosis.
- Stage D (Advanced): Severe symptoms persist despite aggressive treatment. Options at this stage may include mechanical heart pumps or transplant evaluation.
By Functional Ability
Separately, the New York Heart Association grades how much heart failure limits your daily life. Unlike disease stages, functional class can improve or worsen with treatment and time. Class I means no limitation at all during normal activity. Class II means ordinary activity like walking uphill or doing housework causes fatigue or breathlessness. Class III means even light activity, less than what most people consider “ordinary,” triggers symptoms. Class IV means symptoms are present even at rest, and any physical activity makes them worse.
How It’s Diagnosed
Diagnosis typically starts with your symptoms and a physical exam, where a doctor listens for fluid in your lungs and checks for swelling. An echocardiogram, essentially an ultrasound of the heart, provides the ejection fraction measurement and shows whether the walls are thickened, thinned, or moving abnormally.
Blood tests play a key role. Your body releases specific proteins called natriuretic peptides when the heart is under strain. One common marker, NT-proBNP, has different normal thresholds depending on your age. In younger adults, levels below 125 pg/mL generally rule out heart failure as the cause of symptoms. For diagnosing acute heart failure in an emergency setting, the diagnostic cutoffs rise with age: roughly 450 pg/mL for people under 50, 900 pg/mL for those between 50 and 75, and 1,800 pg/mL for people over 75.
Treatment Approach
For the reduced-ejection-fraction type, treatment now rests on four classes of medication that together form what cardiologists call the “four pillars.” Each targets a different pathway that contributes to heart failure progression. One combination drug blocks harmful hormonal signals while boosting the body’s natural protective peptides. Beta-blockers slow the heart rate and reduce the workload. A third class blocks a hormone called aldosterone that drives fluid retention and scarring in the heart. The fourth, originally developed for diabetes, helps the kidneys remove excess sodium and fluid while offering direct protective effects on the heart muscle. Together, these medications improve symptoms, reduce hospitalizations, and extend life.
For preserved-ejection-fraction heart failure, treatment has historically focused on managing the underlying conditions (controlling blood pressure, managing diabetes, losing weight) rather than the heart failure itself. The kidney-protective class of drugs mentioned above is now showing benefit in this type as well, marking the first real pharmacological breakthrough for these patients.
Beyond medications, devices like implantable defibrillators can protect against dangerous heart rhythms, and specialized pacemakers can help the heart’s chambers beat in sync. For people in Stage D whose symptoms persist despite every available treatment, a mechanical pump implanted in the heart (a ventricular assist device) can take over much of the pumping work, either as a long-term solution or as a bridge while waiting for a heart transplant.
Living With Heart Failure
Daily monitoring is one of the most practical things you can do. Weighing yourself every morning, at the same time and on the same scale, helps catch fluid buildup before it becomes a crisis. A gain of more than 2 to 3 pounds in a single day, or more than 5 pounds in a week, is a signal to contact your care team. That kind of rapid weight change almost always reflects fluid retention, not body fat.
Sodium restriction matters because salt drives fluid retention. Most people with heart failure are advised to stay well under 2,000 milligrams of sodium per day. Fluid intake may also be limited in more advanced cases. Regular physical activity, within the limits of your functional class, improves exercise tolerance and quality of life. Cardiac rehabilitation programs are specifically designed to help people with heart failure build endurance safely.
Heart failure is a chronic condition, but it is not a fixed sentence. Ejection fraction can improve with the right treatment, sometimes dramatically. The “improved EF” category exists precisely because a meaningful number of people see their heart function recover enough to reclassify. Early diagnosis, consistent medication use, and active self-monitoring give you the best chance of staying in a lower functional class and avoiding hospitalizations.