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The Causes of Abdominal Fluid Buildup in Cats

A cat with a swollen stomach might have a condition called ascites. What causes this abdominal fluid buildup, and how is it treated?

Melvin Pena  |  Sep 11th 2015

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, or ascites, in cats.

Ascites in cats

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, but any dramatic shift in appetite, weight, body temperature, excremental function, or physical sensitivity during a belly rub might indicate excess abdominal fluid in a cat. Fluid buildup in the abdomen eventually creates so much pressure inside the cat’s body that the cat might have trouble breathing as well.

abdominal fluid causes in cats

A cat with a distended or bloated stomach might have excess fluid buildup. Photo by fat cat on Flickr.

Unfortunately, ascites 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 fluid buildup. The major cat diseases and afflictions that can cause a cat these kinds of stomach pains that we’ll cover here include:

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

Let’s look at each in its turn.

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 fluid buildup and discomfort. 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

Feline infectious peritonitis 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.

abdominal fluid causes in cats

This cat has feline infectious peritonitis. Photo via Wikimedia Commons.

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 is a condition in which the heart is unable or incapable of doing this. CHF in cats has a number of potential causes itself:

  • Heart diseases, such as hypertrophic cardiomyopathy, a thickening of the heart muscle
  • Heartworms
  • High blood pressure

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.


Cancer is another potential cause for abdominal fluid buildup and swelling 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.

abdominal fluid causes in cats

A veterinarian examines a cat’s abdomen for signs of discomfort and swelling. Photo by Shutterstock.

An accurate diagnosis is critical

Before the excess fluid buildup in a cat’s abdomen can be 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 the swelling.

Can abdominal fluid buildup be treated?

Nurturing a cat afflicted with ascites back to health 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.

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.