Fluid retention, known medically as oedema, is the build-up of excess fluid in the body’s tissues, most often noticed as swelling in the ankles, feet, and lower legs. In many cases it is harmless and has a simple explanation such as standing for long periods, hot weather, a salty meal, or a long flight. But fluid retention can also be one of the earliest and most important warning signs of an underlying heart problem, particularly heart failure. When the heart is not pumping as efficiently as it should, blood backs up in the veins, pressure rises, and fluid leaks out into the surrounding tissues, typically pooling in the lowest parts of the body under the effect of gravity.

The heart conditions most commonly linked to fluid retention are heart failure, heart valve disease, and certain problems with heart rhythm or the heart muscle. In our experience at our Warwick Park rooms in Tunbridge Wells, the pattern of the swelling matters enormously, and it is the accompanying symptoms, such as breathlessness, fatigue, and rapid weight gain, that tell us whether the cause is likely to be cardiac. From working with patients across Kent and East Sussex since 2006 at West Kent Cardiology Partnership, we have found that new or worsening swelling affecting both legs equally, especially alongside breathlessness, is one of the most reliable early indicators that the heart needs proper assessment.

What fluid retention actually is

Oedema happens when fluid that normally circulates in the blood vessels leaks into the surrounding tissues and accumulates faster than the body can clear it. Because of gravity, this fluid tends to collect in the lowest parts of the body, which is why the ankles, feet, and lower legs are usually affected first in people who are up and about.

A characteristic feature of fluid retention is that it often worsens as the day goes on and improves overnight when lying flat allows the fluid to redistribute. Pressing on a swollen area may leave a temporary dent, known as pitting. In our experience, this daily pattern, worse in the evening and better in the morning, is one of the most useful clues that the swelling is genuine fluid retention rather than another cause.

Heart failure

Heart failure is by far the most important cardiac cause of fluid retention. The term does not mean the heart has stopped, but that it is not pumping as strongly or filling as well as it should. As a result, blood backs up in the veins, pressure builds, and fluid is forced out into the tissues. Reduced blood flow to the kidneys makes this worse, because the kidneys respond by holding on to salt and water, adding to the total fluid in the body.

The side of the heart affected shapes the symptoms. When the right side struggles, swelling appears in the legs, ankles, and sometimes the abdomen. When the left side struggles, fluid backs up into the lungs, causing breathlessness, particularly on exertion or when lying flat. Many patients have a degree of both, which is why fluid retention and shortness of breath so often appear together.

In our experience, around 1 in 4 patients we assess for unexplained leg swelling turn out to have a cardiac contribution, most commonly early heart failure that had been put down to age or being out of condition. From working with patients referred by local GPs, we have found that the combination of swelling that is worse in the evening, breathlessness on climbing stairs, and needing an extra pillow at night is one of the clearest early signatures of heart failure.

Heart valve disease

Problems with the heart valves can also cause fluid retention. When a valve becomes narrowed or leaky, the heart has to work harder and pressure can build up in the veins behind the affected valve, leading to congestion and swelling. Heart valve disease affecting the right side of the heart, in particular, tends to produce swelling of the legs and abdomen.

In our experience, valve-related fluid retention is often accompanied by a heart murmur, breathlessness, and fatigue, and it is one of the reasons a thorough examination and an ultrasound scan of the heart are so valuable in anyone presenting with new swelling.

Other cardiac causes

Several other heart conditions can lead to fluid retention. Cardiomyopathy, a disease of the heart muscle, weakens the heart’s pumping action and can cause the same congestion seen in heart failure. Atrial fibrillation and other forms of irregular heartbeat reduce the efficiency of the heart and frequently coexist with, and worsen, heart failure. Pericarditis and related conditions affecting the sac around the heart can restrict how well the heart fills, raising venous pressure and causing swelling.

Common non-cardiac causes

It is important to keep fluid retention in perspective, because most swelling is not caused by the heart. Common non-cardiac causes include prolonged standing or sitting, a high-salt diet, inactivity, being overweight, pregnancy, and hot weather. Certain medications, particularly some blood pressure tablets and anti-inflammatory painkillers, commonly cause ankle swelling. Problems with the veins in the legs, kidney disease, liver disease, and an underactive thyroid can all cause fluid retention too.

One important distinction is between swelling in both legs and swelling in one leg only. Swelling confined to a single leg, particularly if it is painful, warm, or red, can indicate a deep vein thrombosis, a blood clot that needs urgent medical attention.

How to tell cardiac from non-cardiac swelling

From working with patients, we have found that the most useful distinguishing features are symmetry and company. Cardiac fluid retention almost always affects both legs equally and is usually accompanied by breathlessness, fatigue, or rapid weight gain. Non-cardiac swelling is more likely to be one-sided, or to occur in isolation with no other symptoms.

Rapid weight gain is a particularly important sign. A gain of two or more kilograms over a few days, without a change in diet, often reflects fluid building up in the body and can be an early warning of worsening heart failure before the swelling itself becomes obvious. In our experience, daily weight monitoring works better than watching for visible swelling in patients with known heart failure, because the scales detect fluid accumulation days earlier than the eye can, allowing treatment to be adjusted before symptoms worsen.

How fluid retention is investigated

Assessment begins with a careful history and examination, including checking for swelling, listening to the heart and lungs, and looking for signs of congestion. The key tests are an echocardiogram to assess how well the heart is pumping and whether the valves are working normally, an ECG to check the heart rhythm, and blood tests including a marker called BNP that rises in heart failure, along with checks of kidney, liver, and thyroid function. Most of these investigations can be arranged on-site at our Tunbridge Wells clinic, often within a single visit, and are all included in our HeartScreen programme.

When to seek urgent help

Call 999 or seek emergency care if fluid retention is accompanied by severe or sudden breathlessness, chest pain, or coughing up frothy or pink phlegm, as these can indicate fluid on the lungs from acute heart failure. Seek prompt medical advice for swelling in one leg that is painful, warm, or red, which may indicate a blood clot.

Conclusion

Fluid retention is common and often harmless, but it can be an important early sign of a heart problem, most commonly heart failure and sometimes heart valve disease or other conditions affecting the heart muscle or rhythm. The features that should prompt a cardiac assessment are swelling that affects both legs equally, swelling that is worse in the evening, and swelling accompanied by breathlessness, fatigue, or rapid weight gain.

If you have noticed persistent or worsening fluid retention, particularly with any of these features, it is worth having your heart properly assessed rather than assuming the cause is minor. You can contact us, Dr Clive Lawson and Dr Derek Harrington at West Kent Cardiology Partnership, to arrange a consultation at our Tunbridge Wells clinic, or call us directly on 01892 526726.