**2. Aetiology**

When a clinician is faced with a dog, which is presented with pericardial effusion, the first challenge is to identify its aetiology. The aetiology of pericardial effusion is idiopathic (unknown cause), congestive heart failure, infectious, neoplasia (cancer), congenital and others (atrial rupture, systemic, hypothyroidism, rarely cirrhosis, etc.).
