A fat cat lying down showing off his stomach.
A fat cat lying down showing off his stomach. Photography © sdominick | iStock / Getty Images Plus.

The Causes of Ascites in Cats (A.K.A. Abdominal Fluid Buildup in Cats)

A cat with a swollen or bloated stomach may have ascites. What causes abdominal fluid buildup in cats? How can ascites in cats be treated?


Does your cat have a bloated stomach? A cat’s abdomen and internal organs are sheathed in a tissue lining called the peritoneum. This lining secretes fluid — peritoneal fluid — which permits everything inside to move comfortably as the cat moves. If your cat suddenly develops belly swelling or abdominal distension, it might indicate any one of a wide array of potentially life-threatening cat health issues due to excess fluid buildup. Depending on the specific issue, this fluid might be overproduced peritoneal fluid, internal bleeding, urine or a combination. Let’s examine some of the major causes of abdominal fluid buildup in cats, or ascites in cats.

Ascites in cats

Overweight cats are at an increased risk for diabetes, which can lead to dry, flaky coats. Photography ©adogslifephoto | Getty Images.
What causes ascites in cats, or swollen stomachs in cats? Photography ©adogslifephoto | Getty Images.

On the most basic level, swelling due to internal fluid buildup is called an edema. When it affects the abdomen or stomach area specifically, it is referred to as ascites. A swollen stomach is one of the most obvious symptoms of ascites in cats, but any dramatic shift in appetite, weight, body temperature, excremental function or physical sensitivity during a belly rub might indicate excess abdominal fluid in cats, or ascites in cats. Fluid buildup in the abdomen eventually creates so much pressure inside the cat’s body that the cat might have trouble breathing as well.

Unfortunately, ascites in cats itself is only a symptom of a larger problem. To determine a course of treatment and hopefully a resolution, a veterinarian needs to determine the precise reason for ascites in cats. The major cat diseases and afflictions that can cause ascites in cats that we’ll cover here include:

  • Abdominal organ failure
  • Cancer
  • Feline infectious peritonitis
  • Physical trauma
  • Right-sided heart failure

Let’s look at each cause of ascites in cats right here:

Abdominal organ failure

Damage to or failure of any the organs in a cat’s abdominal cavity — especially the liver, kidneys and bladder — can each lead to discomfort and ascites in cats. When healthy, these organs provide vital functions including conversion and metabolization of nutrients, filtration, and waste removal. Failures or ruptures of the liver and kidney can release fluid into the abdomen that can become septic.

Liver and kidney failure in cats can occur for a number of similar reasons: ingestion of chemicals or toxins, excessive heat, dietary imbalances, infection, metabolic dysfunction, and anything else that disrupts normal operation. A ruptured bladder can be caused by urinary tract infection, blockages of the urinary tract or disease. With no place for urine to go, the bladder can tear and release urine into the abdomen, irritating the peritoneum, which releases more fluid.

Feline infectious peritonitis

Another cause of ascites in cats, feline infectious peritonitis — or FIP — is caused by a virus that thrives in white blood cells. The name peritonitis gives you the clearest indication that it directly and adversely affects and inflames a cat’s abdominal lining.

There are two forms of FIP in cats, and the one that causes swelling of the peritoneum is effusive, also called wet. When the virus mutates and becomes active, it impairs a cat’s immune system and particularly affects the kidneys and abdominal lining. FIP is a dangerous condition in cats, because it is not only difficult to diagnose, but also practically impossible to cure.

Congestive heart failure on the right side

The right side of the heart is crucial to that organ’s function. It pumps fresh, oxygenated blood through a cat’s body. Congestive heart failure — or CHF — is a condition in which the heart is unable or incapable of doing this. CHF in cats has a number of potential causes itself:

Right-sided congestive heart failure can be genetic and affect younger cats, but it tends to affect older, senior cats more frequently. As a cat’s heart struggles to distribute fresh blood, fluids begin to build up throughout the body, including the abdomen, which leads to ascites in cats.


Cancer is another potential cause for ascites in cats. Tumors or masses anywhere in a cat’s abdominal cavity can lead to blockages and disruption of normal organ functioning. Fluids that should be filtered by any of these organs might either back up or leak out into the abdomen.

Physical trauma

Any kind of physical trauma to a cat’s body — either because of accident, abuse or other causes of injury — can damage internal organs. Whether that’s a tear or rupture to a vital organ that causes internal hemorrhaging of the fluids utilized or processed by them, or of blood, the result is leakage into the abdomen of things that shouldn’t be there. The peritoneum is irritated, excess fluid is produced, and swelling occurs.

An accurate diagnosis for ascites in cats is critical

Before the excess fluid buildup from ascites in cats is treated, an accurate diagnosis is needed. A veterinarian might conduct any of a number of tests, including a physical examination of the cat’s abdomen to check for pain or discomfort caused by external pressure, tests on a cat’s blood and urine, X-rays, and ultrasounds.

The scans might reveal which organ or system is affected, while the blood and urine tests can determine chemical imbalances or reveal infectious agents. The fluid present in the abdomen might also be tapped and tested to find the cause of ascites in cats.

Can ascites in cats be treated?

Treating ascites in cats depends greatly on the root cause of the fluid buildup. Simply draining the fluid might provide temporary comfort to a cat, but if the source of the buildup is not addressed directly, the peritoneum will continue producing fluid, and the abdominal swelling will return. Many of the major reasons we’ve outlined above are extremely serious health issues for cats.

In the case of something like feline infectious peritonitis, and the only real options are geared toward relief rather than cure. As for heartworm infestations, by the time there are sufficient parasites to cause congestive heart failure, it might be too late to treat. If an abdominal cancer is found, treatment options and recovery depend on how advanced the disease is when diagnosed. Performed in time, surgery might be able to resolve physical injury or organ trauma such as a ruptured bladder. Medication might address any bacterial infection that is causing excess fluid production.

This piece was originally published in 2015. 

Thumbnail: Photography © sdominick | iStock / Getty Images Plus.

About the author:

Melvin Peña trained as a scholar and teacher of 18th-century British literature before turning his research and writing skills to puppies and kittens. He enjoys making art, hiking, and concert-going, as well as dazzling crowds with operatic karaoke performances. He has a one-year-old female Bluetick Coonhound mix named Idris, and his online life is conveniently encapsulated here.

Read more about cat health and care here:

24 thoughts on “The Causes of Ascites in Cats (A.K.A. Abdominal Fluid Buildup in Cats)”

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  5. Hi just noticed my cats belly got bigger or looked swollen although she did not seem to have gained weight. She urinates regularly, eat and drink as usual but one thing I am worried is that she used to poop 3 or 4 x a day but have not seen her do that since yesterday. Is there any thing I can do at this point as the vet here is also expensive…

    1. Hi there,
      Please contact a vet ASAP about this! The articles below might help, but it sounds like your cat really needs vet attention:

  6. My cat is 16-17 years old and recently started loosing weight and has a very swollen firm belly. The vet took blood tests everything was clear apart from hear murmur and low thyroid. I don’t understand how she is so thin and also the huge belly is causing difficulty in breathing. She eats drinks and loves being cuddle someone please help as the vet won’t give me answers .

  7. A feral female cat I care for that is spayed and has severe hyperesthesia where she scratches and licks her neck area so that it is raw, has started to look like she’s pregnant. I did a search and it appears to be a form of abdominal fluid buildup. Is it possible this is caused by the hyperesthesia? She has a good appetite and doesn’t exhibit any signs of being ill. But, I wonder if it’s a result of causing injury to herself, perhaps a blood infection. Unfortunately, she’s not friendly enough to touch so I can’t put her in a carrier. She was spayed by a TNR group 3 yrs ago.

    1. Hi there Joanna,

      Thanks for reaching out! We suggest contacting your vet with this question. We hope your cat feels better!

  8. I found the reading material to be very helpful, so much concerns I have for my cat now, i have brought her into the vets to have some bloodwork done I also explained about her breathing and they just ignored It, should I have a urine test done as well and how do it retrieve her urine, please help me out thank you.

  9. I’m so worried overnight my older cat’s belly has swollen she doesn’t want me to touch it I love her she’s over 10 years old I don’t have the money to take her to the vet for 2 weeks when I get paid she’s been part of my daughters life for over half her life do u no of anything I can do to help her call me cat it’s my nick name

    1. Hi there — Could you at least call your vet and describe the symptoms? We can only provide advice and insight, not medical diagnosis, unfortunately.

      These pieces might help if you’re struggling to afford vet care:

      Hope your kitty feels better!

    2. See if your vet takes Care Credit. My vet does. It’s a credit card only for medical stuff. My dentist takes it too,lol. Anyway it’s great because anything put on it is interest free if you pay it off within a few months (can’t remember if it is 3 or 6 months).

  10. Hi. My cat does not have such a swollen belly as the one in the picture thankfully. However, her right side has been swollen for a while. I’ve been trying to take her to the vets but it is expensive unfortunately. Thankfully she does not seem bothered if I touch that side. I know cats are not supposed to display signs of pain but she doesn’t seem to care if I stroke the right side of her belly. Could it be any of the things listed above? Thanks in advance.

  11. Hi,I log on to your new stuff named “The Causes of Abdominal Fluid Buildup in Cats – Catster” like every week.Your humoristic style is awesome, keep up the good work! And you can look our website about اغاني.

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