Pericardial Effusion In Dogs

Written by Shula Berg BVSc CertAVP(GSAS) GPAdvCert(SASTS) MRCVS
Clinically reviewed by Elizabeth McLennan-Green BVM&S CertAVP(SAM) MRCVS

Table of Contents

- Overview
- Symptoms
- Diagnosis
- Treatment
- Outlook

The pericardium is the thin sac that surrounds the heart. A pericardial effusion occurs when the sac fills with fluid, most commonly blood. A small amount of fluid doesn’t cause a problem, however, the pericardium is not very stretchy, so if the effusion grows the pericardium rapidly becomes tense. This means the fluid will start compressing the heart, reducing its ability to beat normally and push oxygenated blood around the body. 

There are several causes of pericardial effusion in dogs. Roughly 60% of pericardial effusions are due to a tumour of the heart, though these can be very challenging to diagnose, so the actual number may be higher. Less common causes include congestive heart failure, blood-clotting disorders, inflammation, or perforation of the heart. In a significant number of cases, no underlying cause is identified; these are known as idiopathic pericardial effusions. 

Any dog can develop a pericardial effusion, but they are seen more commonly in older, large breed dogs such as Golden Retrievers, German Shepherds and Bernese Mountain Dogs. Boxers are predisposed to a particular type of heart tumour. 

What are the symptoms of Pericardial Effusion? 

Symptoms of pericardial effusion are often vague, especially if the fluid builds up gradually. Common symptoms include lethargy and exercise intolerance. Some dogs may be inappetent, vomit or have a cough. If pericardial effusion develops rapidly, the body is unable to cope with the sudden drop in output, and the dog may collapse. 

With chronic effusions, if the heart is not pushing enough blood out around the body, the dog may develop Congestive Heart Failure (CHF). This causes congestion in the blood vessels within the lungs and fluid leaks into the lung tissue, known as Pulmonary Oedema. Less commonly, congestion leads to fluid accumulation in the abdomen (called Ascites) or in the chest cavity around the lungs (known as Pleural Effusion). Dogs in CHF will be weak, lethargic, and may have difficulty breathing. 

Which tests are used to diagnose Pericardial Effusion? 

A pericardial effusion may have no obvious external symptoms. If there is enough fluid present, the heart may sound muffled when listened to with a stethoscope. Pulses may be weak or irregular, and blood pressure is often low. With effusions that have developed slowly, fluid may also accumulate in the abdomen due to pressure on specific parts of the heart. 

A diagnosis of pericardial effusion is made by ultrasound examination of the heart. This demonstrates fluid accumulation in the pericardium, and enables assessment of the degree of effusion present. A thorough heart scan, known as echocardiography or an “echo” is required to look for the presence of tumours. These are often small and difficult to spot, so it is strongly recommended that this is performed by an experienced cardiologist. If possible, they will retrieve a sample of cells using a fine needle to attempt to confirm the tumour type. 

Blood tests may be recommended to check the bloods ability to clot. Some types of tumour frequently spread elsewhere in the body, so it is often advisable to perform an ultrasound of the abdomen to examine the liver and spleen. 

How is Pericardial Effusion treated?

Emergency treatment of pericardial effusion involves draining the fluid out of the pericardial sac, a procedure known as pericardiocentesis. This is performed using a special catheter, with the patient under sedation or anaesthesia. It is a safe procedure, however arrhythmias (irregular heartbeats) can occur, so close monitoring during and afterwards is advisable. Heart tumours are often easier to identify before the effusion is drained, so if the dog is still systemically well, your vet may recommend referral to an experienced cardiologist straight away. 

Further treatment depends on the cause of the pericardial effusion. The most common tumour causing pericardial effusion in dogs is a cancer of the blood vessel lining, known as a Haemangiosarcoma. These are very aggressive and have often spread to other organs at the time of diagnosis. Ultrasound or CT imaging of the chest and abdomen may be advised to look for spread. 

For idiopathic effusions, and slow-growing tumours called Chemodectomas, monitoring only is likely to be advised in the first instance. Many pericardial effusions will recur, but for truly idiopathic effusions, this can often be over a year after first diagnosis. Generally, effusions due to tumours recur faster, so even if no tumour is found on ultrasound, a rapidly recurring effusion should raise suspicion. 

It is recommended that no more than two consecutive pericardial effusions should be drained, as this increases the risk of scar tissue constricting the heart. For dogs whose effusions recur slowly, no tumour is identified, and are otherwise well, surgery can be considered. This is known as a pericardiectomy, and involves removing part of the pericardial sac so that fluid drains into the chest cavity and is absorbed, rather than accumulating and compressing the heart. It is a complex surgery, so is usually performed by a specialist or surgeon with additional training. Some clinics can offer a less invasive keyhole approach. 

What is the outlook for dogs with Pericardial Effusion?

The prognosis for dogs with pericardial effusion is reasonable to guarded depending on the cause. Patients who have Haemangiosarcoma diagnosed have a very poor prognosis, and often euthanasia is considered more appropriate than pericardiocentesis. This is sadly also the case for dogs who are very elderly at diagnosis, or who undergo draining but then experience rapid recurrence (days or weeks). 

Patients who have no identifiable tumour on ultrasound, or whose pericardial effusion doesn’t recur within the first few months, have a reasonable prognosis. The effusion may recur eventually, however, dogs can have an excellent quality of life until this point. Those patients who do undergo surgery for true idiopathic pericardial effusion have a good prognosis post-operatively. As pericardial effusions are more common in older animals, a small number of cases will not experience recurrence of the effusion in their lifetime.   


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Page last reviewed: 3rd March 2024

Next review due: 3rd March 2026