Pericardial effusion (PE) is a common disease of the pericardium in dogs and cats and is characterized by accumulation of increased amount of fluid in the pericardial sac. PE is classified on the basis of physical and cytological characteristics of the pericardial fluid. Pericardial effusion is commonly diagnosed in German Shepherds, Boxer, English bulldog, and Boston Terrier due to various reasons. Clinical signs depend on the rate and degree of cardiac compensation. Moderate cardiac compression causes signs related to right heart failure such as weakness, lethargy, exertion, dyspnea, ascites, and syncope on exertion, while signs of low cardiac output such as marked weakness or collapse, dyspnea/tachypnea, and death develop rapidly in case of severe compression of the heart. Pericardial effusion in dogs is of idiopathic or neoplastic origin (hemangiosarcoma is common). Pericardial disorders are of two main types, i.e., congenital or acquired. Congenital pericardial disorders may be due to diaphragmatic hernia, pericardial cyst, or pericardial defects, while acquired pericardial disorders are further subcategorized as pericardial effusion, constrictive pericarditis, and pericardial mass with or without effusion or fibrosis.