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Small fluid around the heart seen by chance on a scan

An echocardiogram (heart ultrasound) or CT scan done for another reason may report a "small pericardial effusion" or "trace of pericardial fluid". This means there is a little more fluid than usual in the sac around the heart. It is often found by chance on imaging done for something else. (Shanker 2025) This page covers what the report means and the checks guidance lists, not treatment.

What the report means

  • What it is. The pericardium is a sac around the heart. A pericardial effusion is a build-up of fluid in that sac. (MedlinePlus) The sac normally holds about 10 to 50 ml of fluid. (Shanker 2025)
  • Speed matters more than size. Whether fluid causes symptoms depends mainly on how fast it builds up, not only on how much there is. (Shanker 2025)
  • Fat can look like fluid. Fat on the surface of the heart can look similar on a scan; the STAAB study used a set definition to tell them apart. (Sahiti 2024)

How size is described

  • Small: under 10 mm of fluid at its deepest, about 100 ml. (Lazarou 2024)
  • Moderate: 10 to 20 mm, about 100 to 500 ml. (Lazarou 2024)
  • Large: over 20 mm, more than 500 ml. (Lazarou 2024)
  • Which scan. European and American heart imaging guidance names the heart ultrasound as the main test for suspected pericardial fluid. (Sahiti 2024) So a finding on CT is often checked with an echocardiogram.

How common it is and how often it clears

  • About 3 in 100 adults. In the STAAB study of 4,965 adults aged 30 to 79 in Würzburg, Germany, with no heart failure, 134 (2.7%) had fluid around the heart on a heart ultrasound. The median depth was 2.7 mm, 99% were small, and none of the people had symptoms. (Sahiti 2024)
  • Most cleared. At a repeat scan a median of 34 months later, the fluid had gone in 65 of 107 people (61%). (Sahiti 2024)
  • No link to later illness. A small effusion found this way was not linked to inflammation markers, death, new heart failure or a new cancer during follow-up. It was more common in people with a lower body weight. (Sahiti 2024)

Possible causes

  • Often no cause is found. In developed countries up to half of effusions are called idiopathic, meaning no cause is found. (Shanker 2025)(Lazarou 2024)
  • Known causes. These include inflammation of the sac (pericarditis), infections, autoimmune disease, an underactive thyroid, kidney failure, cancer, injury and heart surgery. (Shanker 2025)(MedlinePlus) Pericarditis often follows a viral infection such as a cold or flu. (NHS)

Checks guidance lists next

  • Blood tests. Reviews list C-reactive protein (a marker of inflammation), thyroid-stimulating hormone and troponin, with further tests chosen for the situation. (Lazarou 2024) Others listed include a full blood count, kidney and liver function and an autoimmune screen. (Shanker 2025) See thyroid test results and kidney test results.
  • Repeat heart ultrasound. Whether you need one depends on the size, your symptoms and the cause; see "Where they differ" below. An echocardiogram uses no radiation, which suits repeat checks. (Lazarou 2024)

How it ties to your age-based checks

A small effusion found by chance is a good time to make sure your routine checks are up to date:

Other heart findings have their own pages: mild leaky heart valve on an echocardiogram, enlarged heart on a chest X-ray, thick heart muscle on an ECG or echo and small hole in the heart (PFO).

Who it applies to

Adults told that an echocardiogram or CT done for another reason shows a small amount of fluid around the heart, with no symptoms. Fluid after heart surgery or a heart procedure, during cancer care, or with chest pain or breathlessness is outside this page.

Reviews advise everyone with fluid around the heart to get medical help promptly if symptoms start. (Lazarou 2024) MedlinePlus lists chest pain, a rapid heartbeat and difficulty breathing as symptoms of pericardial problems, and cardiac tamponade, where fluid stops the heart working properly, as a serious problem. (MedlinePlus) The NHS advises an urgent appointment or NHS 111 for sharp chest pain that gets worse when you breathe in or lie down, and to call 999 (911 in the US) for sudden chest pain that spreads to the arms, back, neck or jaw, feels tight or heavy, or comes with shortness of breath. (NHS)

Routine age-based screening

A finding on a heart scan does not replace the routine screenings for your age. See screenings by age and gender.

Where they differ:

  • Follow-up scans. A 2025 review reports that the 2025 European Society of Cardiology guidance needs no follow-up for a mild effusion with no known cause and no symptoms. (Shanker 2025) A 2024 review, written before that update, suggested a check every 3 to 6 months for small or moderate effusions. (Lazarou 2024) The STAAB authors concluded a small effusion without symptoms does not need close short-term monitoring. (Sahiti 2024)
  • How common. The Framingham study in 1983 reported 6.5%, while STAAB found 2.7%; the STAAB authors note the older definition likely counted fat as well as fluid. Framingham also found more effusions with age, which STAAB did not. (Sahiti 2024)
  • Outlook. Small effusions with no known cause are generally thought to have an excellent outlook, though the 2024 review notes not all studies agree. (Lazarou 2024)

Your doctor decides what your result means for you.

Questions people ask

How common is a little fluid around the heart?

In a German population study of 4,965 adults aged 30 to 79 with no heart failure, 2.7% had a small amount of fluid on a heart ultrasound, none of them with symptoms. (Sahiti 2024)

Does it go away?

Often. In the same study, the fluid had cleared in 61% of people who had a repeat scan about three years later. (Sahiti 2024)

Is it a sign of cancer or heart failure?

In that study, a small effusion found by chance was not linked to death, new heart failure or a new cancer over about three years. Your doctor decides whether your history needs more checks. (Sahiti 2024)

What blood tests might be done?

Reviews list C-reactive protein (inflammation), thyroid-stimulating hormone (thyroid), troponin, kidney and liver function and, in some cases, autoimmune tests, chosen to fit the situation. (Lazarou 2024) (Shanker 2025)

Will I need another scan?

It depends on size, symptoms and cause. A 2025 review reports that the 2025 ESC guidance needs no follow-up for a mild effusion with no known cause and no symptoms; an earlier review suggested a check every 3 to 6 months for small or moderate effusions. Your doctor decides. (Shanker 2025) (Lazarou 2024)

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