What heart problems might leg swelling indicate?

Leg swelling can point to several heart problems, with heart failure being by far the most common cardiac cause. When the heart can't pump efficiently, blood backs up in the veins and fluid is pushed out into the surrounding tissue, settling under gravity into the ankles, feet, and lower legs. Other cardiac causes include valve disease (especially right-sided problems), poorly controlled atrial fibrillation, pulmonary hypertension, and pericardial disease. That said, not every swollen ankle is a heart issue. In our experience, around half the patients we assess for leg swelling turn out to have a non-cardiac cause such as venous insufficiency or a medication side effect. The reason it still warrants checking is that the cardiac causes tend to be progressive, and they respond far better to treatment when caught early.

If you've been searching because your legs or ankles have started swelling and you want to know what it means, here's the short version. Mild puffiness at the end of a long day on your feet, in hot weather, or after a long flight is usually harmless. Swelling that is already there when you wake, doesn't settle when you raise your legs, affects both legs roughly equally, or arrives alongside breathlessness, tiredness, or unexplained weight gain is the kind that points towards the heart and should be assessed. The pattern of the swelling tells us more than the swelling itself.

Why Heart Problems Cause Leg Swelling

When the heart is working well, blood returning from the legs flows easily back to the right side of the heart, through the lungs, and out around the body. When that pump weakens, or the right heart has to strain against high pressure, fluid leaks from the smallest blood vessels into the tissue, and gravity draws it down into the lower limbs.

This is known as dependent oedema, and it has a recognisable signature. It is typically worst by evening, often eases overnight while you're lying flat, and leaves a dent when pressed firmly with a finger, which is called pitting oedema. The NHS guidance on swollen ankles, feet and legs sets out the wider picture.

Heart Failure, The Main Cardiac Cause

Heart failure is the leading cardiac reason for leg swelling. Right-sided heart failure causes the most visible lower-limb swelling, because the right ventricle struggles to move blood through the lungs and pressure backs up into the body's veins. Left-sided heart failure tends to flood the lungs first but eventually drives leg swelling too.

It rarely shows up on its own. Most patients also notice breathlessness on exertion or when lying flat, unusual fatigue, weight gain of a kilogram or two over a few days as fluid builds, and sometimes a heart that feels like it's pounding once they're in bed as the body works harder to compensate. The British Heart Foundation's heart failure information covers the full presentation.

From working with patients across South West London and the South-East over the past decade, we've found that roughly 60% of those who arrive with swelling in both legs plus any degree of breathlessness have at least early-stage heart failure once assessed. Identifying it at that point genuinely changes the treatment and the long-term outlook.

Other Cardiac Causes of Leg Swelling

Valve disease. Right-sided valve problems, particularly tricuspid regurgitation, raise pressure in the venous system and produce swelling. Severe left-sided disease such as aortic valve disease or mitral valve disease eventually pushes right-sided pressure up too. The BHF's heart valve disease page explains how a failing valve causes symptoms over time.

Atrial fibrillation. Sustained, poorly controlled atrial fibrillation can lower cardiac output and lead to fluid retention, especially in older patients. The NHS information on atrial fibrillation outlines how it affects the heart's pumping.

Pericardial disease. Pericarditis, particularly the constrictive form, stops the heart filling properly and congests the venous system. Swelling here often comes with chest discomfort that worsens on lying flat.

Pulmonary hypertension. High pressure in the lung arteries forces the right ventricle to work against resistance, and over time it tires, causing swelling and breathlessness.

Non-Cardiac Causes Worth Considering

Plenty of leg swelling has nothing to do with the heart. Common culprits include venous insufficiency and varicose veins, lymphoedema, kidney disease, liver disease, medications such as calcium channel blockers and anti-inflammatories, pregnancy, and simply standing or sitting for long stretches.

In our experience, the single most useful question is whether one leg is affected or both. One-sided swelling is far more often venous, lymphatic, or a clot. Swelling that is even on both sides is more likely to be cardiac, kidney-related, or drug-induced, and calls for a broader assessment. Sudden swelling in one leg with calf pain or warmth can signal a deep vein thrombosis, and the NHS guidance on DVT explains when that needs urgent attention.

When to Seek Urgent Help

Seek urgent assessment, or call 999, if leg swelling comes with:

• Sudden or severe breathlessness

• Chest pain or tightness

• Coughing up pink, frothy fluid

• Confusion or fainting

• Sudden one-sided swelling with calf pain or warmth

• A rapid jump in weight over a few days

For swelling that is more gradual but persistent, a planned cardiology assessment within a week or two is the sensible route.

How We Investigate Leg Swelling at Heartsure

Across more than a decade of running diagnostic cardiology in Kingston-upon-Thames, we've completed in excess of 12,000 cardiac investigations, and leg swelling is one of the more revealing reasons people are referred, because it frequently uncovers a condition nobody had spotted.

A first appointment pairs a detailed history and consultant assessment with a 12-lead ECG and an echocardiogram to check pump function, the valves, and the right heart. Bloods through our diagnostic blood testing service cover BNP or NT-proBNP (a marker of heart strain), kidney and liver function, thyroid function, and a full blood count. Where blood pressure may be playing a part, a 24-hour blood pressure monitor gives a far truer reading than a single clinic measurement.

In our experience, an echocardiogram paired with BNP testing works better than an echocardiogram alone for catching early heart failure, because BNP picks up ventricular strain before it shows as a structural change on the scan. We've found that around a quarter of patients with leg swelling and an apparently normal echocardiogram have a raised BNP indicating early heart failure with preserved ejection fraction, and those cases would slip through on imaging alone. Where we suspect reduced coronary blood flow, a CT coronary angiogram or myocardial perfusion scan gives a non-invasive answer.

Practical Steps to Take Before Your Appointment

A few simple things help us reach an answer faster.

Weigh yourself each morning for a fortnight and note any sharp changes. A gain of more than 1.5 kg over three days is a meaningful sign of fluid retention. Photograph the swelling first thing and again last thing at night, since the contrast shows how gravity-driven it is. List every medication, including over-the-counter painkillers and supplements, because several common drugs cause swelling and ruling them out is often the first useful step. Finally, note any breathlessness on stairs or when lying flat, as that shifts our diagnostic priority.

Conclusion

Leg swelling has many possible causes, and the cardiac ones, including heart failure, valve disease, atrial fibrillation, and pericardial disease, are worth identifying early because they respond well to treatment within the right window. The pattern of the swelling, whether it affects one leg or both, when in the day it peaks, and what other symptoms travel with it are the strongest clues to whether the heart is involved. A proper assessment combining consultation, ECG, blood tests, and an echocardiogram gets most patients to a confident answer quickly.

If you've noticed leg swelling and want to understand what might be behind it, you can contact Heartsure on 0208 255 5999, email info@heartsure.co.uk, get in touch through our contact page, or book an appointment online. Our team in Kingston-upon-Thames offers same-day appointments where clinically appropriate, and most patients are seen within the same week as their first enquiry.