Pleural Effusion in Cats (Fluid Around the Lungs)

Jennifer Coates, DVM
By Jennifer Coates, DVM on Mar. 17, 2023

In This Article


What Is Pleural Effusion in Cats?

For cats to breathe easily, their lungs need to be able to fill with air and expand. A buildup of fluid between the lungs and the chest wall can stop this from happening. This condition is called pleural effusion, and it can be life-threatening if not dealt with quickly.

The pleura are thin membranes that cover the outside of the lungs and the inside of the chest cavity. Normally a tiny amount of fluid is present to help keep the pleura healthy and act as a lubricant when the lungs inflate and deflate.

Many health problems can lead to more fluid collecting between the pleural membranes. Small amounts of pleural effusion may not have much of an effect, but a lot of extra fluid will significantly reduce a cat’s lung capacity.

Pleural effusion is different from pulmonary edema. Both conditions can make it hard for cats to breathe, but pleural effusion is fluid around the lungs while pulmonary edema is the buildup of fluid within lung tissue. The causes and treatments for pleural effusion and pulmonary edema are also different.

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Symptoms of Pleural Effusion in Cats

Cats with pleural effusion typically have a combination of the following symptoms:

  • Rapid breathing

  • Shallow breathing

  • Working harder than normal to breathe

  • Open-mouth breathing

  • Coughing

  • Lethargy

Depending on how long the effusion has been present, how severe it is, and its underlying cause, you may also notice:

Take your cat to a veterinarian or emergency clinic immediately if they are having trouble breathing or the symptoms seemed to come on suddenly. Your cat’s life may be in danger if you wait too long.

On the other hand, mild symptoms that come on slowly (over the course of days or weeks rather than hours) are rarely an emergency. Call your regular veterinarian for advice if your cat doesn’t seem to be in distress, particularly if you already know the cause of your cat’s pleural effusion. You can also chat with a veterinary expert through Chewy’s Connect With a Vet service for insight on next steps.

Causes of Pleural Effusion in Cats

A study published in 2018 revealed the most common causes of pleural effusion in cats. Combined, these six conditions made up almost 95% of the cases of pleural effusion.

  • Congestive heart failure (40.8%): Advanced hypertrophic cardiomyopathy and other diseases that affect heart muscle often lead to congestive heart failure. This is the most common cause of pleural effusion in cats.

  • Cancer (25.8%): Lymphoma, carcinoma, and other types of cancer within the chest cavity can lead to pleural effusion.

  • Pyothorax (14.5%): Infections may result in a buildup of pus inside the chest cavity, which is called a pyothorax.

  • Idiopathic chylothorax (6.3%): Chyle is a milky liquid that is formed in the intestines. It transports fats and other substances around the body. Cats will be diagnosed with idiopathic chylothorax when, for no apparent reason, chyle leaks out of a duct that normally drains into a large blood vessel in the chest.

  • Trauma (4.2%): Being hit by a car, falling off a balcony, being attacked by a dog, or other traumatic injuries can lead to bleeding within the chest cavity or a rupture of the duct that carries chyle.

  • Feline infectious peritonitis (3.2%): Young cats that have a protein-rich fluid within their chest or abdominal cavities are often diagnosed with feline infectious peritonitis (FIP).

Most of these conditions are very serious. Rapid diagnosis and treatment are important for improving a cat’s prognosis and quality of life.

How Veterinarians Diagnose Pleural Effusion in Cats

Cats that are having trouble breathing may need emergency care to stabilize their condition before a veterinarian can start looking for an underlying cause. The doctor may give your cat oxygen or do a chest tap to remove pleural effusion, which will allow their lungs to better fill with air.

When it’s safe to do so, the veterinarian will perform a physical examination and ask you about your cat’s health history, including any symptoms you’ve seen at home, when they started, and how they’ve progressed. They will also want to know if your cat goes outside or could have been injured indoors.

Diagnostic testing is usually needed to figure out exactly what is causing a cat’s pleural effusion. This may include:

  • Examining a sample of the pleural effusion

  • Chest X-rays

  • Ultrasound of the heart, lungs, and chest cavity

  • Advanced imaging like a CT scan or MRI

  • A blood chemistry panel, complete blood cell count, and other lab work

Treatment of Pleural Effusion in Cats

Often, a chest tap is the first line of treatment if a pleural effusion is greatly affecting a cat’s ability to breathe. Chest taps do not merely help diagnose the underlying cause; they can also give immediate symptomatic relief. These chest taps can be repeated if fluid returns, or the veterinarian may place a chest tube in your cat to allow for more continuous drainage.

Recovery and Management of Pleural Effusion in Cats

Additional treatments will focus on treating or managing the cat’s underlying health problem.

  • Congestive heart failure in cats can usually be managed with medications that improve heart function and symptoms.

  • Cancer is often treated with chemotherapy, surgery, radiotherapy, immunotherapy, or palliative care. The right combination of treatments depends on the specifics of a cat’s case.

  • Pyothorax that is caused by a bacterial infection will usually respond to antibiotic therapy combined with drainage of the fluid.

  • Idiopathic chylothorax treatment can include feeding a low-fat diet and medications that decrease the flow of chyle. Surgery may also be necessary to tie off the duct that carries chyle into the chest cavity.

  • Traumatic injuries may heal on their own with rest, pain relief, and other types of symptomatic and supportive care, but surgery is needed in some cases.

  • FIP is usually fatal, but symptomatic and supportive care may improve a cat’s quality of life. New treatments are being developed and may be available in specific cases. Talk to your veterinarian about options.


Ruiz MD, Vessières F, Ragetly GR, Hernandez JL. Characterization of and factors associated with causes of pleural effusion in cats. Journal of the American Veterinary Medical Association. 2018;253(2):181-187.

Krentz D, Zenger K, Alberer M, et al. Curing Cats with Feline Infectious Peritonitis with an Oral Multi-Component Drug Containing GS-441524. Viruses. November 2021;13(11):2228.

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Jennifer Coates, DVM


Jennifer Coates, DVM


Dr. Jennifer Coates is an accomplished veterinarian, writer, editor, and consultant with years of experience in the fields of veterinary...

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