CONDITION

Pericardial Effusion

Pericardial effusion involves accumulation of fluid within the sac surrounding the heart, which can compress the heart and impair its function, presenting with signs of cardiovascular compromise.

Why this matters now

Pericardial effusion typically affects middle-aged to older dogs, with large and giant breeds showing increased susceptibility. The condition can develop gradually or accumulate rapidly, with sudden presentations sometimes occurring as the first indication of underlying disease.

As fluid accumulates in the pericardial sac, pressure on the heart increases. Initially, the heart may compensate, but as volume grows, the right side of the heart becomes compressed, impairing its ability to fill with blood. This leads to backing up of blood in the venous system and reduced forward blood flow, causing the clinical signs of right-sided heart failure.

Signals & patterns

Early signals

Exercise intolerance

Reduced stamina and reluctance to engage in normal activity may reflect compromised heart function.

Mild lethargy

General decrease in energy levels as cardiovascular efficiency declines.

Reduced appetite

Dogs may eat less as blood flow to digestive organs decreases.

Occasional coughing

May occur though less prominent than with other heart conditions.

Later signals

Abdominal distension

Fluid accumulates in the abdomen (ascites) as blood backs up in the venous system.

Laboured breathing

Respiratory effort increases as body demands more oxygen than compromised circulation can deliver.

Pale gums

Reduced blood flow causes the mucous membranes to appear pale rather than healthy pink.

Collapse episodes

Sudden weakness or fainting may occur, particularly with exertion or excitement.

Click to read about the biological mechanisms

How this is usually investigated

Diagnosis combines clinical findings suggesting right-sided heart failure with imaging to confirm fluid presence and identify potential underlying causes.

Echocardiography

Purpose: Visualises fluid around the heart, assesses cardiac compression, and may identify masses
Considerations: The gold standard for diagnosis; shows real-time heart function; can guide drainage procedures.

Chest radiographs

Purpose: May reveal an enlarged, globe-shaped heart silhouette and other chest abnormalities
Considerations: Supportive but not definitive; helps assess lungs; may miss small effusions.

Electrocardiogram (ECG)

Purpose: Can show characteristic changes associated with pericardial effusion
Considerations: Low-voltage complexes and electrical alternans suggest effusion; quick bedside test.

Pericardiocentesis with fluid analysis

Purpose: Removes fluid for patient relief and diagnostic examination
Considerations: Therapeutic and diagnostic; fluid characteristics help identify cause; cytology may reveal tumour cells.

Abdominal ultrasound

Purpose: Checks for primary tumours or metastatic disease
Considerations: Important staging tool if cancer suspected; assesses liver and spleen.

Cardiac troponin levels

Purpose: Blood marker that may help distinguish tumour-related from inflammatory causes
Considerations: Higher levels tend to correlate with neoplastic causes; not definitive alone.

Options & trade-offs

Management depends on the underlying cause and ranges from emergency fluid drainage to long-term surgical options, with prognosis varying significantly based on aetiology.

Pericardiocentesis

Needle drainage of fluid from the pericardial sac, often guided by ultrasound

Trade-offs: Immediately relieves tamponade; can be repeated if fluid recurs; carries some procedural risk.

Pericardiectomy

Surgical removal of part of the pericardium to prevent future fluid accumulation

Trade-offs: Can provide lasting solution for idiopathic cases; major surgery; prognosis depends on cause.

Treatment of underlying cancer

Chemotherapy for responsive tumour types when cancer is the cause

Trade-offs: May extend quality time; effectiveness varies with tumour type; hemangiosarcoma carries guarded prognosis.

Anti-inflammatory therapy

Medications for idiopathic or inflammatory pericarditis

Trade-offs: May reduce fluid production; generally well tolerated; not effective for neoplastic causes.

Supportive care

Diuretics, rest restriction, and monitoring for recurrence

Trade-offs: Manages secondary effects; buying time while determining next steps.

Common misconceptions

Misconception:

"Pericardial effusion always means cancer"

Reality:

While cardiac tumours are a common cause, idiopathic pericarditis accounts for a significant proportion of cases and carries a much better prognosis.

Misconception:

"Once drained, the problem is solved"

Reality:

Fluid often reaccumulates, particularly with ongoing underlying disease; monitoring and potentially further intervention may be needed.

Misconception:

"Dogs with pericardial effusion are always obviously unwell"

Reality:

Gradual accumulation allows adaptation; some dogs present with subtle signs before acute decompensation.

Owners of large-breed dogs showing signs of exercise intolerance, abdominal swelling, or collapse episodes may find value in cardiovascular assessment. Understanding that both the severity and the underlying cause influence prognosis can help guide discussions about investigation and treatment options.

Last reviewed: 24 April 2026 · Dr Alastair Greenway MRCVS