If Your Dog Has a Swollen Belly and Lethargy — Symptoms of Pericardial Effusion and Emergency Timing

HeartDiseasesMeongsiljang Veterinary Advisory Board

Pericardial effusion in dogs is a heart condition in which fluid abnormally accumulates in the sac surrounding the heart. We’ve compiled the essential information pet owners need to know, covering symptoms, diagnosis, treatment, and home care.

What Is Canine Pericardial Effusion?

A scene of a puppy undergoing an echocardiogram (heart ultrasound) examination.

Canine pericardial effusion is a heart condition in which abnormal fluid accumulates within the thin sac surrounding the heart (the pericardium), interfering with the heart's ability to contract and relax. When large amounts of fluid build up, it can lead to cardiac tamponade, a life-threatening emergency. If you notice signs such as rapid breathing, a distended abdomen, or reluctance to exercise, seeking immediate veterinary care is essential. This condition occurs more frequently in large-breed and senior dogs, and tumors are a common underlying cause.

Main Causes of Pericardial Effusion

The causes of pericardial effusion are broadly categorized into neoplastic and non-neoplastic.

Hemangiosarcoma: This is a malignant tumor that develops in the heart, particularly in the right atrium. It is especially common in German Shepherds (particularly those over 7 years old), Golden Retrievers, and Labrador Retrievers, and is the most frequent neoplastic cause of pericardial effusion in dogs.

Base of the Heart Tumors (Aortic Body Tumors): These tumors originate at the base of the aorta and are relatively more commonly reported in brachycephalic breeds.

Idiopathic (Unknown Cause): This refers to cases where a specific cause cannot be identified. Alongside tumors, idiopathic causes are among the most common reasons for hemorrhagic pericardial effusion.

Pericarditis: Infectious inflammation, such as that caused by fungal infections, can be a cause. Bacterial (purulent) pericarditis is relatively rare.

Other Causes: Other reported causes include trauma, coagulopathies (such as anticoagulant rodenticide poisoning), left atrial rupture, and renal failure.

Checklist of Main Symptoms of Canine Pericardial Effusion

Rapid breathing: Your pet may breathe quickly and shallowly or pant with an open mouth.

Abdominal distension: As pericardial effusion progresses, fluid can accumulate in the abdomen, causing it to swell.

Reluctance to move or lethargy: Your pet may tire easily with minimal activity or prefer to lie down constantly.

Fainting or collapse: Severe compression of the heart can lead to sudden collapse or loss of consciousness.

Pale gums: Reduced blood circulation may cause the gums to appear pale or grayish.

Weak pulse: A decreased cardiac output can result in a weak and irregular pulse.

Signs That Require Immediate Emergency Care

If your pet is breathing only through its mouth, suddenly collapses, or has pale or bluish gums, seek emergency veterinary care immediately. Cardiac tamponade is a life-threatening emergency that can be fatal within hours. Do not delay treatment, even on nights or holidays.

Diagnostic Methods — What Tests Will Be Performed?

Physical examination and auscultation: If heart sounds are quieter and more distant than normal, pericardial effusion should be suspected.

Thoracic radiographs (X-rays): The cardiac silhouette may appear abnormally enlarged or take on a "water-bottle" shape.

Echocardiography (ultrasound): This is the most accurate diagnostic method, allowing direct visualization of the volume, location, and cause of fluid within the pericardial sac.

Blood and biochemical tests: These evaluate the patient’s overall systemic health and help assess for underlying infection or neoplasia.

Pericardial fluid cytology: Analysis of the aspirated fluid confirms the presence of tumor cells or bacterial infection.

Treatment Methods — Step-by-Step Procedures

Pericardiocentesis: This is an emergency procedure in which a needle is used to drain fluid from the pericardial sac, immediately relieving pressure on the heart and restoring normal blood circulation.

Medication: Depending on the underlying cause, medications such as antibiotics, anti-inflammatory drugs, or steroids may be administered under veterinary guidance.

Pericardiectomy: If pericardial effusion recurs frequently or is caused by a tumor, surgery may be performed to remove part of the pericardial sac.

Cancer Treatment: If a tumor, such as hemangiosarcoma, is identified as the cause, your veterinarian may recommend chemotherapy in consultation with a veterinary oncologist.

Home Care Management Points

Maintain calm: For at least 1–2 weeks after returning home, avoid vigorous exercise and allow your pet to rest in a quiet environment.

Diet and medication management: Unlike typical congestive heart failure, diuretics and vasodilators are not recommended for pericardial effusion. Therefore, always manage diet and medications strictly according to your veterinarian’s prescription and instructions, and never administer any medication without professional guidance.

Medication administration: Give prescribed medications exactly as scheduled, without missing doses. Do not stop or add any medication without consulting your veterinarian.

Regular follow-up exams: Since fluid reaccumulation (recurrent effusion) is common after pericardiocentesis, it is essential to have echocardiograms performed at the intervals specified by your veterinarian.

Symptom monitoring: Contact your clinic immediately if you notice rapid breathing or if your pet’s abdomen becomes distended again.

Important Information for Owners of Large Breeds and Specific Breeds

Breeds such as German Shepherds, Golden Retrievers, and Labrador Retrievers have a higher risk of developing right atrial hemangiosarcoma, which is particularly common in dogs aged seven years and older. Brachycephalic breeds like Boxers and French Bulldogs have a relatively higher risk of tumors at the base of the aorta (aortic body). If you own one of these breeds, consider discussing regular cardiac ultrasound screenings with your veterinarian, even if your dog shows no symptoms.

Reviewed by a veterinarian

Dr. Tony — Punnawat Phongkittirak

Veterinarian

A veterinarian who majored in veterinary medicine at Khon Kaen University, Thailand, and completed the IVSA program at North Carolina State University in the United States. Drawing on clinical experience at animal hospitals, he works in the pet healthcare field and is dedicated to building a digital care environment that connects pet parents with veterinarians.

Frequently Asked Questions

Can pericardial effusion recur?

Yes, recurrence is possible. If only pericardiocentesis was performed, fluid tends to reaccumulate in most cases, regardless of whether the underlying cause is a tumor or idiopathic. To prevent repeated episodes, surgical management such as pericardiectomy may be necessary, so please be sure to discuss a regular follow-up schedule with your veterinarian.

Can my pet be discharged immediately after pericardiocentesis?

If your pet’s condition is stable right after treatment, same-day discharge may be possible. Depending on the underlying cause and overall health status, hospitalization for observation for one day or longer may be necessary.

Is idiopathic pericardial effusion curable?

While idiopathic cases generally have a relatively favorable prognosis, fluid often reaccumulates after pericardiocentesis alone. If this happens repeatedly, a pericardiectomy can be beneficial for long-term management. Additionally, since some cases may progress to chronic constrictive pericarditis, regular check-ups are essential.

When can my pet start exercising after treatment?

During the acute phase, your pet should rest completely. Once their condition has stabilized, consult your veterinarian before gradually starting with short, gentle walks. Sudden, intense exercise can put a strain on the heart.

Does pericardial effusion affect life expectancy?

The prognosis varies significantly depending on the underlying cause. While idiopathic cases tend to have a relatively favorable outlook, the prognosis can be more limited when the cause is hemangiosarcoma. Early detection and appropriate treatment have the greatest impact on your pet’s quality of life.

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References

[1] Ehrhart N, Withrow SJ. Pericardial Disease and Cardiac Neoplasia. In: Veterinary Surgical Oncology, 2nd Ed. Wiley-Blackwell, 2020.

[2] de Laforcade AM, Freeman LM, Rozanski EA, et al. Biochemical analysis of pericardial fluid and whole blood in dogs with pericardial effusion. J Vet Intern Med 19(6):833–836, 2005.

[3] Dunning D, Monnet E, Orton EC, et al. Analysis of pericardial fluid and whole blood for diagnosis of neoplastic disease in dogs with pericardial effusion. Vet Surg 27(5):525–526, 1998.

[4] Tobias KM, Johnston SA (eds). Veterinary Surgery: Small Animal, 2nd Ed. Elsevier, 2018.