In a healthy pericardium, there are two layers of membranous tissue that are separated by a thin, serous fluid (pericardial fluid) that keeps both the layers and the heart lubricated. When the pericardium becomes inflamed, it is an indication that the layers are beginning to unnaturally stiffen and thicken. The body’s membranes will produce excess fluid in response, but instead of the fluid absorbing back into the body as it should, it accumulates within the pericardium. This places constrictive pressure on the right side of the heart and prevents it from functioning properly. Without immediate treatment, even more inflammation (cardiomyopathy) and more serious complications will occur including, in some cases, the two layers adhering to each other and eliminating the pericardial fluid space. 

Inflammation of the heart sac (pericardium) is also known as pericarditis and pericardial effusion. It is a chronic condition that develops slowly over time and can result in permanent scarring and muscle tightening in the right side of the heart if it is not treated right away. While it is possible for the condition to occur in cats, pericarditis along with effusion is not common. However, if effusion is present, it is usually a complication that is in response to an underlying systemic disease such as infection or myocardial disease.

Since cats are not commonly afflicted with pericarditis, the symptoms may not be evident until heart failure has occurred. However, there are certain signs to watch for.

There are several types of pericarditis depending on the origination of the condition. The most common are:

The cause of pericarditis in cats can be either congenital or acquired, and sometimes there is no apparent cause at all. Usually, the cause is not determined until the time of diagnosis. Causes that have been associated with pericarditis are:

Your veterinarian will first conduct a thorough physical exam including listening to your cat’s heart. Your veterinarian may conduct a urinalysis and measure your cat’s electrolyte levels, and he or she may draw blood to conduct a complete blood count. Your veterinarian will also want to conduct a series of tests. 

An electrocardiogram will be performed to determine how the heart is functioning. The test will measure the heart’s blood pressure and flow, strength, and any arrhythmia. This test is mostly helpful when there is a high volume of effusion. It is the most sensitive, non-invasive test for pericardial effusion.

X-rays will be taken to detect any tumors as well as effusion and its severity. However, if no effusion is apparent, it does not necessarily mean that it is not there. This is, therefore, not always a reliable diagnostic test, but it can be helpful in reviewing clinical evidence.

An ultrasound may be taken to detect small amounts of effusion plus any underlying pericardial disease, blood clots, and masses. It will also allow your veterinarian to determine if there is an atrial rupture and the thickness of the pericardium.

An analysis of the pericardial fluid may be performed to help determine the presence of infection due to microorganisms. This test is important, especially when thickening has been found.

This is the most accurate test for pericarditis and effusion, but it is also the most invasive. It involves threading a tube through an artery or vein of an arm or leg and up to the chambers of the heart. The heart’s pressure is monitored to determine its functionality.

Your cat will need to be immediately hospitalized and prepared for surgery. Often, the best treatment is a pericardiocentesis in which the excess fluid surrounding the heart is drained to relieve pressure on the heart. This fluid will be tested for the presence of infection, microorganisms, cancer, and blood (see Fluid Analysis in “Diagnosis”). 

A partial pericardiectomy where the affected, thickened portions of the pericardium are surgically removed is also sometimes necessary. It is conducted through a procedure called a thoracoscopy where a small window is opened into the pericardium in order to remove the thickened tissue. Your veterinarian will take this opportunity to also explore more of the areas surrounding the heart for signs of any underlying disease. 

If the layers of the pericardium are found to be adhering to each other, your veterinarian may want to attempt to separate them so as to relieve constriction on the heart. This is a highly risky procedure, however, and your veterinarian should discuss it with you before it is performed. 

It is important to note that in most cases a pericardiectomy is usually sufficient and most effective in relieving constriction, as opposed to attempting to separate the pericardial layers. 

If cancer was determined during diagnosis, chemotherapy will be administered, and if any infections were detected the appropriate antibiotics will be prescribed. 

If a diaphragmatic hernia was determined to be the cause of microorganisms leaking into the pericardium, appropriate measures will be taken to repair the hole(s).

Your veterinarian will schedule a follow-up appointment with you to assess how your cat is responding to treatment and to further discuss any ongoing treatment options, especially if your cat was determined to have a systemic infectious disease or cancer. Additional x-rays and ultrasound may also be taken.

Antibiotics and chemotherapy may continue to be necessary depending on the cause of the pericarditis. Additional medications may also be necessary to treat any other cardiac conditions. 

Success in treating pericarditis and pericardial effusion is entirely based on the quickness in diagnosing the condition and administering proper treatment, especially if thickening and hardening of the pericardium has already begun and constriction is apparent. 

The prognosis for pericarditis and pericardial effusion is generally good. However, the condition can reoccur, especially if the pericardium was able to be left intact. Though the excess fluid may be relieved and heart function restored, constriction on the heart due to additional or new adhering of the layers of the pericardium may still occur. If this is the case, then further treatment is required since the prognosis at this point is usually poor.

Typically, you should see signs of improvement after surgery such as greater exercise tolerance and overall outward behavior within a week. But if your cat exhibits any signs of reoccurrence at any time, contact your veterinarian immediately.