Pericardial effusion is a common problem in older dogs. The problem arises from accumulation of fluid within the pericardial sac, a membrane surrounding the heart. The accumulation of fluid compresses the heart and prevents the heart from beating normally. As a consequence, right sided heart failure occurs which manifests as fluid build up around the lungs and in the abdomen resulting in coughing, trouble breathing, lethargy and abdominal distension. The two most common causes for this problem are tumours or from an idiopathic/unknown factor. The fluid must be drained under sedation and this temporarily relieves the pressure on the heart. A keyhole surgery is also available as a long term treatment options to prevent future fluid accumulation in this sac.
Attached is an xray of a dog with a pericardial effusion. The heart appears very large and round