Heart failure is a serious medical condition, but the term “heart failure” does not mean that the heart has stopped working. It means the heart is unable to pump or fill well enough to meet the body’s needs. It can develop gradually or appear suddenly, and symptoms can range from mild breathlessness during exercise to significant symptoms even while resting.
Importantly, heart failure is not simply divided into “mild, moderate and severe.” Doctors commonly use two different systems to describe it: Stages A–D, which describe the progression of the disease, and NYHA Classes I–IV, which describe how much symptoms limit a person’s physical activity.
Stage A: At Risk of Heart Failure
Stage A is the earliest stage.
A person in Stage A does not have heart failure symptoms or structural/functional heart disease, but has factors that increase their risk of developing heart failure.
These can include:
- High blood pressure
- Diabetes
- Obesity
- Coronary artery disease
- A family or genetic risk of cardiomyopathy
- Exposure to certain treatments or substances that can damage the heart
At this point, prevention is particularly important. Controlling blood pressure, managing diabetes and maintaining a heart-healthy lifestyle can help reduce the risk of progressing to heart failure.
Stage B: Pre-Heart Failure
Stage B is sometimes called “pre-heart failure.”
Here, there is already evidence of a problem involving the heart, but the person has not developed heart-failure symptoms.
For example, there may be structural heart disease, reduced heart function, valve disease or evidence that the heart is experiencing increased filling pressure. Certain blood-test abnormalities can also contribute to the classification.
This stage is important because a person may feel completely normal while changes are already occurring in the heart.
Stage C: Symptomatic Heart Failure
Stage C is where a person has structural heart disease and has experienced current or previous symptoms of heart failure.
Symptoms can include:
- Shortness of breath
- Fatigue
- Reduced ability to exercise
- Persistent cough
- Swelling of the feet, ankles or legs
- Swelling around the abdomen
- Difficulty breathing when lying down
- Weight gain caused by fluid retention
Symptoms can vary considerably from one person to another.
Someone at Stage C may still be able to work, exercise and live relatively normally, particularly when treatment is controlling their symptoms.
Stage D: Advanced Heart Failure
Stage D is advanced heart failure.
At this stage, heart-failure symptoms significantly interfere with everyday life and may be difficult to control despite treatment. Some people experience repeated hospitalizations.
People with advanced heart failure may require specialist care and, depending on their individual circumstances, treatments such as specialized devices, mechanical heart pumps or evaluation for transplantation.
But There Is Another Classification: NYHA Classes I–IV
The A–D stages tell doctors where someone is in the disease process. The NYHA classification tells them how much the symptoms affect physical activity.
Class I – No Significant Limitation
The person has no significant limitation during ordinary physical activity.
Normal activities do not cause unusual fatigue, shortness of breath or other heart-failure symptoms.
Class II – Mild Limitation
The person is comfortable at rest, but ordinary physical activity can cause symptoms such as:
- Breathlessness
- Fatigue
- Palpitations
- Chest discomfort
Class III – Significant Limitation
The person is comfortable while resting, but less-than-normal physical activity produces symptoms.
For example, activities that previously seemed easy may now cause considerable fatigue or breathlessness.
Class IV – Symptoms Even at Rest
This is the most severe NYHA functional class.
The person may experience heart-failure symptoms even while resting, and almost any physical activity can make the symptoms worse.
Stage and Class Are Not the Same Thing
This distinction is important.
A doctor might describe someone as:
Stage C, NYHA Class II
That means the person has symptomatic heart failure, but their symptoms currently cause only a mild limitation of physical activity.
Another person could have:
Stage D, NYHA Class IV
That indicates advanced heart failure with severe functional limitation and symptoms that may occur at rest.
The NYHA class can also change with treatment, so it isn’t necessarily permanent.
What About Ejection Fraction?
Another term people often hear is ejection fraction (EF).
EF measures how much blood the left ventricle pumps out with each contraction. An echocardiogram is commonly used to measure it.
However, ejection fraction alone does not tell the entire story about the severity of heart failure. Someone can have significant heart-failure symptoms even when their EF is not severely reduced.
This is why doctors consider symptoms, physical examination, imaging, blood tests, medical history and other findings when assessing heart failure.
Heart Failure Does Not Mean There Is Nothing That Can Be Done
A diagnosis of heart failure is serious, but treatment can help many people manage symptoms and live longer, more active lives. Treatment depends on the type and severity of heart failure and may include medications, lifestyle changes, devices or procedures.
The key message is that early detection matters. Stage A and Stage B provide opportunities to identify risk and heart abnormalities before symptomatic heart failure develops.
Final Thoughts
Heart failure is better understood as a spectrum rather than a single condition. The journey can progress from being at risk (Stage A), to having evidence of heart disease without symptoms (Stage B), to symptomatic heart failure (Stage C), and in some people to advanced disease (Stage D).
Understanding these stages can help patients and families understand what doctors mean when they discuss “the stage” or “class” of heart failure—and why controlling risk factors and seeking medical care early can be so important.
Note: The staging system has been refined in a 2026 international consensus document, so a patient’s exact classification should be determined by their healthcare professional rather than by symptoms alone.
