How do doctors work out which type of heart failure I have? 

Heart failure is not a one-size-fits-all diagnosis. While the symptoms, breathlessness, fatigue, and swelling, are often the same, the underlying reason why the heart is struggling can vary significantly. Some hearts are weak and cannot squeeze, while others are stiff and cannot fill. Working out exactly which type you have is the most important part of the diagnostic process because it dictates which medications will work for you. In the UK, doctors use a combination of your clinical history, blood tests, and detailed heart scans to categorise your condition. 

What We’ll Discuss in This Article 

• The primary distinction between HFrEF and HFpEF 

• How the Ejection Fraction (EF) percentage is calculated 

• The role of the echocardiogram in assessing heart stiffness 

• Why your medical history (past heart attacks vs high blood pressure) provides clues 

• The difference between left-sided and right-sided heart failure 

• Advanced tests like Cardiac MRI for muscle characterisation 

• When to seek urgent medical advice 

The Gold Standard: Ejection Fraction (EF) 

The most important way doctors categorise heart failure is by measuring your Ejection Fraction during an echocardiogram (heart ultrasound). This is a measurement of how much blood the left ventricle—the heart’s main pumping chamber, pumps out with each contraction. 

How it is categorised: 

• HFrEF (Reduced EF): The EF is 40% or less. The heart muscle is typically weak, thinned, and stretched. This is often caused by a past heart attack. 

• HFmrEF (Mildly Reduced EF): The EF is between 41% and 49%. This is a ‘middle ground’ where the heart is starting to show weakness. 

• HFpEF (Preserved EF): The EF is 50% or higher. The heart appears to pump normally, but the muscle is often thick and stiff, meaning it cannot relax to let enough blood in. 

Assessing Heart Stiffness vs Weakness 

If your scan shows a normal pumping percentage (HFpEF), doctors must look for more subtle signs to confirm heart failure. This is often more difficult to diagnose than the ‘weak’ type. 

Signs of Stiffness (HFpEF): 

• Left Atrial Enlargement: Because the bottom chamber is stiff, the top chamber (the atrium) has to work harder to push blood down, causing it to stretch and grow. 

• Diastolic Dysfunction: The sonographer uses Doppler ultrasound to measure the speed of blood flow into the heart. If the blood moves at an unusual speed, it suggests the heart muscle is not relaxing properly. 

• NT-proBNP Levels: According to the British Heart Foundation, if you have symptoms and a raised blood test but a ‘normal’ pump, stiffness is the likely culprit. 

Left-Sided vs Right-Sided Failure 

Doctors also look at which side of the heart is primarily affected, as this changes where fluid builds up in your body. 

• Left-Sided Failure: The most common type. Fluid backs up into the lungs, causing breathlessness and a cough. 

• Right-Sided Failure: Often caused by left-sided failure or lung disease. Fluid backs up into the body, causing swollen ankles, legs, and a bloated abdomen. 

• Congestive Heart Failure: This is the term used when both sides are failing and fluid is building up throughout the system. 

Using Medical History as a Map 

Your past health issues provide a roadmap for doctors to guess the type of heart failure before the scans are even finished. 

Clinical Clue	Likely Type of Heart Failure
Past Heart Attack	HFrEF (Weak muscle due to scarring)
Long-term High Blood Pressure	HFpEF (Stiff muscle due to pressure strain)
Heart Valve Disease	Can be either, depending on whether the valve is leaky or narrowed
Heavy Alcohol Use	HFrEF (Toxic weakening of the muscle)

Advanced Characterisation 

In complex cases, an echo might not be enough. Your doctor may request a Cardiac MRI. This scan uses ‘Late Gadolinium Enhancement’ to see the exact pattern of any scarring. 

• Inner wall scarring: Confirms the cause was a lack of blood flow (ischaemic). 

• Patchy or outer wall scarring: Suggests the cause was a virus (myocarditis) or a genetic condition. 

According to the NHS, getting this specific diagnosis is vital because certain modern drugs, like SGLT2 inhibitors, have different levels of evidence depending on your specific EF percentage. 

Conclusion 

Doctors work out your type of heart failure by looking at three main things: how well the heart squeezes (EF), how well it relaxes (stiffness), and which side of the pump is most affected. The echocardiogram is the essential tool for this, but your medical history of blood pressure or heart attacks provides the context. Knowing whether your heart is weak or just stiff allows your medical team to choose the right ‘noble’ path for your treatment, ensuring the medications you take are the ones proven to help your specific heart. 

Emergency Guidance 

If you have a diagnosis but suddenly find you cannot breathe while lying flat, or you begin coughing up pink frothy mucus, call 999 immediately. This is acute decompensation, regardless of your heart failure type. 

FAQ Section 

Authority Snapshot 

This article was written by Dr. Rebecca Fernandez, a UK-trained physician with extensive experience in cardiology, internal medicine, and emergency care. Dr. Fernandez has managed critically ill patients and provided comprehensive inpatient care within the NHS framework. This guide strictly follows NICE and NHS diagnostic protocols to explain how medical teams differentiate between the various forms of heart failure.