---
title: Pericardial effusion
description: What a pericardial effusion is — extra fluid in the sac around the heart — why it develops, what symptoms a small and a large effusion cause, how it is found and treated, and when to call an ambulance.
type: disease
aliases:
  - fluid around the heart
  - hydropericardium
sources:
  - tier: guideline
    org: minzdrav-rf
    title: Перикардиты
    year: 2025
    url: https://cr.minzdrav.gov.ru/view-cr/746_2
  - tier: guideline
    org: esc
    title: 2025 ESC Guidelines for the management of myocarditis and pericarditis
    year: 2025
    doi: 10.1093/eurheartj/ehaf192
    url: https://doi.org/10.1093/eurheartj/ehaf192
  - tier: reference
    org: msd-manuals
    title: Pericarditis
    year: 2026
    url: https://www.msdmanuals.com/professional/cardiovascular-disorders/myocarditis-and-pericarditis/pericarditis
sources_checked: 2026-10-13
review: null
---

A pericardial effusion is a build-up of fluid in the pericardium, the sac around the heart. The fluid may be serous, mixed with blood, or it may be blood, pus or chyle (lymph).<Cite n={[1, 3]} /> Normally the pericardium holds only a little fluid, up to 15–50 mL.<Cite n={1} /> An effusion can come with inflammation of the pericardium — [pericarditis](../pericarditis/) — but it also develops without inflammation, for example in severe heart failure.<Cite n={1} /> A small effusion usually causes no symptoms.<Cite n={1} /> The dangerous kind is an effusion that stops the heart from filling with blood: that is [cardiac tamponade](../cardiac-tamponade/).<Cite n={3} />

<Diagram name="pericardial-effusion">
  <p slot="normal">
    The pericardium has two layers: an inner (visceral) and an outer (parietal) one. Between them
    is a closed, slit-like cavity with a small amount of fluid that lubricates the
    layers.<Cite n={1} />
  </p>
  <p slot="disease">
    With an effusion there is more fluid between the layers of the pericardium than
    normal.<Cite n={[1, 3]} /> Its size is judged on ultrasound by the distance between the layers.<Cite n={[1, 2]} /> A
    small effusion usually causes no symptoms; if the fluid stops the heart from filling, that is
    tamponade.<Cite n={[1, 3]} />
  </p>
</Diagram>

## Why it happens

<Patient>

When the pericardium is inflamed, inflammatory fluid forms inside it. The causes of the inflammation are described in the article on [pericarditis](../pericarditis/).<Cite n={1} /> In severe [heart failure](../heart-failure/) or [pulmonary hypertension](../pulmonary-hypertension/) the pressure in the veins is raised, so fluid is absorbed back less well and collects between the layers of the pericardium.<Cite n={1} />

Cancer is the most common cause of an effusion large enough to affect the circulation.<Cite n={1} /> An effusion can also appear after chemotherapy or radiotherapy.<Cite n={1} /> Other causes are an underactive thyroid (hypothyroidism) and severe kidney disease.<Cite n={[1, 3]} />

Effusions are common after heart surgery.<Cite n={1} /> Blood can collect in the pericardium after a chest injury, after heart procedures such as fitting a pacemaker or cardiac catheterisation, and when an aortic aneurysm ruptures.<Cite n={[1, 3]} />

</Patient>

<Student>

Inflammation of the pericardium leads to an exudate; in severe chronic heart failure and/or marked pulmonary hypertension, reduced reabsorption due to raised systemic venous pressure leads to a transudate.<Cite n={1} /> The Russian Ministry of Health guideline uses the term hydropericardium specifically for an excessive accumulation of transudate.<Cite n={1} />

The ESC classifies an effusion by onset (acute, up to 4 weeks; subacute, over 4 weeks and up to 3 months; chronic, over 3 months), size (mild, moderate, large), distribution (circumferential or loculated) and composition (transudate or exudate).<Cite n={2} /> The cause of the effusion is known in about 50% of cases.<Cite n={1} />

After heart surgery, effusions occur in 25–30% of cases, in the first days after the operation; in 10% of cases they are large and may lead to tamponade, most often within the first day and usually because of bleeding.<Cite n={1} /> In the first days of a [myocardial infarction](../myocardial-infarction/), an effusion is linked to acute heart failure and shrinks as it resolves; an effusion over 10 mm should raise suspicion of an evolving myocardial rupture.<Cite n={1} /> In post-MI syndrome, usually within 10 days to 2 months after the infarction, an effusion occurs together with fever, pleural inflammation and joint pain.<Cite n={3} />

In people with cancer an effusion develops in 5–15%, more often at a late stage.<Cite n={1} /> Chronic pericarditis with a large effusion is most commonly caused by metastatic tumours, most often lung or breast carcinoma, sarcoma, melanoma, leukaemia or lymphoma.<Cite n={3} /> Hypothyroidism is the most common endocrine cause of hydropericardium; the fluid accumulates slowly, so tamponade is rare.<Cite n={1} />

</Student>

## Symptoms

<Patient>

Symptoms depend on the size of the effusion. A small effusion usually causes none.<Cite n={1} /> With a moderate one, breathlessness builds up — first on exertion, then at rest — together with a dull, aching pain behind the breastbone and a feeling of fullness or distension.<Cite n={1} /> If a large effusion affects how the heart works, blood pressure falls, and dizziness and palpitations appear.<Cite n={1} />

A large effusion that grows slowly can press on nearby organs: this causes nausea and poor appetite, difficulty swallowing, a hoarse voice and hiccups.<Cite n={1} /> The effusion itself is often painless; pain occurs when it comes with acute pericarditis.<Cite n={3} />

</Patient>

<Student>

Arterial pulse, jugular venous pulse and blood pressure are normal unless intrapericardial pressure rises substantially and tamponade develops.<Cite n={3} /> A large effusion muffles the heart sounds and enlarges the area of cardiac dullness; compression of the base of the left lung reduces breath sounds near the left scapula and causes crackles.<Cite n={[1, 3]} /> A pericardial rub may be heard.<Cite n={3} />

Tamponade develops when a moderate or large effusion impairs cardiac filling.<Cite n={3} /> If the effusion is not very large, whether tamponade develops depends on how fast the fluid accumulates, not on how much there is.<Cite n={1} /> The signs of tamponade are described in [its article](../cardiac-tamponade/).

</Student>

## How it is diagnosed

<Patient>

An effusion is often first suspected when a chest X-ray shows an enlarged heart shadow.<Cite n={3} /> The main test is a [heart ultrasound (echocardiography)](../../diagnostic/echocardiography/): it confirms the effusion, shows its size and helps to detect tamponade.<Cite n={3} /> An [ECG](../../diagnostic/ecg/) and blood tests are also done, including markers of inflammation.<Cite n={[1, 2]} /> If the effusion does not seem to be caused by inflammation, a thyroid hormone test (TSH) is done.<Cite n={1} />

Sometimes fluid is taken from the pericardium for testing to find the cause.<Cite n={[1, 2]} />

</Patient>

<Student>

In the ESC algorithm, first-line assessment of an effusion includes history, physical examination, ECG, chest X-ray, transthoracic echocardiography and laboratory assessment.<Cite n={2} /> When an effusion is suspected, the Russian Ministry of Health guideline recommends a full blood count, biochemistry and C-reactive protein, and TSH when a non-inflammatory effusion is suspected; in an effusion of unknown origin, thyroid function should be assessed first, even without signs of hypothyroidism.<Cite n={1} />

On the ECG, QRS voltage is often reduced and most patients remain in sinus rhythm; with large, chronic effusions there may be electrical alternans, associated with a swinging heart.<Cite n={3} /> The amount of fluid is assessed on echocardiography in diastole by the distance between the layers.<Cite n={1} /> An effusion under 10 mm is mild, 10–20 mm moderate and over 20 mm large.<Cite n={[1, 2]} /> CT is recommended to evaluate pericardial thickness, calcifications, masses and loculated effusions (I C).<Cite n={2} /> CT may overestimate the size of an effusion and is not a first-line test.<Cite n={3} />

Analysis of pericardial fluid — cells, total protein, albumin and LDH — distinguishes an exudate from a transudate; cytology and tumour markers are examined to rule out a malignant effusion.<Cite n={1} /> A haemorrhagic effusion is usually associated with malignancy and also occurs after heart surgery, after trauma, and in autoimmune and viral pericarditis.<Cite n={1} /> If tuberculosis is possible, acid-fast staining and culture of the fluid are essential.<Cite n={3} />

</Student>

## How it is treated

<Patient>

Treatment is aimed first of all at the cause of the effusion.<Cite n={[1, 3]} /> If the effusion is linked to inflammation, it is treated in the same way as [pericarditis](../pericarditis/).<Cite n={1} /> A small effusion without worrying signs may be watched by the doctor with repeat heart ultrasounds.<Cite n={3} />

In tamponade, when a cancer or bacterial cause is suspected, and when a moderate or large effusion causes symptoms despite treatment, the fluid is drained through a needle (pericardiocentesis) guided by ultrasound, CT or X-rays.<Cite n={2} /> If the fluid keeps coming back, a surgeon can make a "window" in the pericardium through which it can drain.<Cite n={[1, 2]} /> The doctor decides which approach is needed.

</Patient>

<Student>

In the ESC algorithm, cardiac tamponade or a symptomatic moderate to large effusion with suspected neoplastic or bacterial aetiology calls for admission, pericardiocentesis and a search for the cause.<Cite n={2} /> Otherwise, concomitant pericarditis is treated as pericarditis and an associated systemic disease is treated in its own right; a large (over 20 mm), chronic (over 3 months) symptomatic effusion is managed with pericardiocentesis with drainage and empirical anti-inflammatory therapy; all other cases have outpatient follow-up.<Cite n={2} /> If the fluid re-accumulates and causes symptoms, a pericardial window is created.<Cite n={2} /> If the effusion is not related to inflammation, anti-inflammatory treatment is ineffective; if it grows and the risk of tamponade rises, pericardiocentesis is considered.<Cite n={1} />

Pericardiocentesis is the simplest and quickest way to drain the pericardium; it is performed by an experienced doctor under echocardiographic or fluoroscopic guidance, and complications occur in 4–10% of cases.<Cite n={1} /> The ESC recommends surgical drainage when percutaneous pericardiocentesis is not feasible or the effusion is purulent, to allow complete drainage and prevent constriction, and a surgical pleuro-pericardial window for relapsing effusion despite medical therapy (I C).<Cite n={2} /> The rare effusive–constrictive form of [constrictive pericarditis](../constrictive-pericarditis/) combines an effusion with constriction of the heart: raised right atrial pressure persists after the fluid has been removed.<Cite n={1} />

Treatment depends on the aetiology. In hypothyroidism, replacement therapy is indicated to bring thyroid hormone levels to normal.<Cite n={1} /> Pericarditis due to uraemia may respond to more frequent haemodialysis.<Cite n={3} /> In a neoplastic effusion, cytology of the fluid confirms the diagnosis, and once a neoplastic cause is confirmed, systemic anticancer treatment targets the primary tumour and metastases; when purulent pericarditis is suspected, urgent pericardiocentesis and/or a surgical window is needed.<Cite n={2} /> Untreated, purulent pericarditis is fatal.<Cite n={1} />

Small effusions with pericarditis or without an obvious cause have a good prognosis; idiopathic chronic effusions are complicated by tamponade in one patient in three; bacterial, tuberculous and cancer-related effusions and those in connective tissue disease have a worse prognosis.<Cite n={1} />

</Student>

## When to call an ambulance

An effusion on its own often causes no symptoms; the threat to life is tamponade, when the fluid stops the heart from filling.<Cite n={[1, 3]} /> Call your local emergency number (112 in the EU, 911 in the US and Canada, 999 in the UK) if a person who has an effusion or pericarditis, or who has had heart surgery or a heart procedure, a chest injury or a recent heart attack, develops bouts of sudden severe weakness, dizziness, fainting or worsening breathlessness.<Cite n={[1, 3]} /> Everyone with signs of tamponade is admitted to hospital as an emergency.<Cite n={1} />

As with any heart condition, call an ambulance for fainting, chest pain or severe breathlessness: this is the site's general safety rule, repeated at the bottom of every page.

<Quiz />