The pericardium is the outer sac that surrounds the heart. It is made up of two layers: the delicate inner membrane called the visceral pericardium, or epicardium, and the more fibrous outer layer called the parietal pericardium. There is a small space between these two layers that is filled with about 0.2-0.3 milliliters of fluid for each kilogram of your dog’s weight. The exact function of the pericardium is unknown, but it may help to protect the heart and maintain its normal placement in the thorax. Inflammation of the pericardium, called pericarditis, causes fluid to accumulate in the pericardial sac (pericardial effusion). Excess fluid increases pressure within the pericardium. If outside pressure becomes greater than the normal pressure within the heart, a dangerous condition called cardiac tamponade can develop. With cardiac tamponade, the increased pressure makes it difficult for the heart to contract, and heart failure can happen quickly. Pericardiectomy, surgical removal of the entire pericardium, can be curative depending on the condition that is causing the problem. Primary idiopathic pericardial effusion is the most common cause of pericarditis in dogs, responsible for about 20-70% of cases. With primary pericarditis, the inflammation of the pericardial sac and subsequent pleural effusion does not appear to have a cause. Other forms of pericarditis can be caused by fungal or bacterial infection, but this is rare in dogs. Heart conditions that cause pericardial disease through fluid accumulation have similar symptoms to inflammatory pericarditis. Of these, cancer is the most common in dogs, accounting for 70-80% of the cases of cardiac tamponade from severe pericardial effusion. Some inherited abnormalities, tearing or injury to the mitral valve on the left side of the heart, and rarely congestive heart failure can also be responsible for pericardial disease These conditions are indistinguishable symptomatically from inflammatory pericarditis since they all cause pericardial effusion.

Inflammation of the heart sac, the pericardium, causes fluid to accumulate between the inner and outer layers. In dogs, this is called pericarditis. If the pressure inside the pericardium becomes greater than the pressure inside the heart, this can be very dangerous.

These are the different types of pericardial disease

These are the main causes of pericarditis in dogs.

Other heart conditions may cause non-inflammatory pericardial disease.

The veterinarian will physically examine your dog and listen to his heart. The heartbeat will usually sound muffled through a stethoscope if pericardial effusion is present. Breathing sounds can be difficult to hear also, although the breathing rate is increased. Other symptoms, typical of right-side congestive heart failure, will help to confirm the presence of pericardial effusion. Other diagnostic tests will be necessary for a definitive diagnosis. Chest x rays may show an abnormal heart silhouette with pericardial effusion, but echocardiography, an ultrasound of the heart, is usually a better tool for identifying the source of the problem. Many diseases that are cause pericardial disease can be diagnosed in this way, including cancerous tumors, congenital heart abnormalities, and valve degeneration.  A diagnosis of idiopathic pericarditis is usually made by eliminating all the other factors which could cause pericardial effusion, while infectious pericarditis is identified by examining a fluid sample from the heart with cytology and checking for the presence of bacteria or fungi. Constrictive pericarditis is not common and it can be difficult to diagnose. Measuring the pressure on both sides of the heart is the most reliable method.

Cardiac tamponade is a very serious condition that will require immediate supportive treatment. Pericardiocentesis, insertion of a tube to syphon off the fluid, may be necessary save your dog’s life as continuous elevated intrapericardial pressure can be fatal after only five minutes. If your dog is on diuretic medication for congestive heart failure, this will need to be discontinued since these medications can actually make cardiac tamponade more severe. If fluid accumulation continues to be a problem, pericardiocentesis may be performed several times. Dogs with idiopathic pericarditis may also be given corticosteroid medication to reduce inflammation. If symptoms don’t improve, pericardiectomy, surgical removal of the pericardium may be ordered. Dogs with infectious pericarditis will be given appropriate antibiotic or antifungal medication. Other treatments could be necessary if cancer, or an inherited abnormality like PPHD is causing your dog’s pericardial effusion rather than inflammatory pericarditis.

Dogs with idiopathic, primary pericarditis typically have a good prognosis. About 50% of cases respond to pericardiocentesis alone, and pericardiectomy usually cures those that don’t respond. Constrictive pericarditis can also usually be treated by removal of the thickened pericardium. Effective treatment of infectious pericarditis will depend on eliminating the bacteria or fungi that are causing the infection. The main danger with all types of pericarditis is that cardiac tamponade can become fatal before treatment is possible. Discussing the condition with a veterinarian before it becomes severe is the best way of preventing the problem.