Updated September 25, 2026. Fact-checked against veterinary sources; review by a licensed veterinarian is in progress. See our editorial policy.
Quick answer: Ascites is a buildup of fluid in the abdomen, which makes a dog’s belly look swollen or pot-bellied. It isn’t a disease on its own but a sign of an underlying problem, most often heart failure, liver disease, low blood protein from kidney or gut disease, cancer, or internal bleeding. Any dog with a swelling belly needs a vet visit. A sudden swollen belly with weakness, pale gums, or collapse is an emergency.
Signs
- A swollen, rounded, or sagging belly that may feel like a water balloon
- Weight gain around the middle while the back and legs look thin
- Faster or harder breathing, especially lying down
- Tiredness, poor appetite, or reluctance to exercise
- Discomfort when lying down or being picked up
Emergency signs
Go to an emergency vet immediately if your dog’s belly swells suddenly, especially with pale gums, weakness, collapse, or fast breathing. This can mean internal bleeding, for example from a ruptured spleen tumor. A tight, swollen belly with unproductive retching may be bloat, also an emergency.
Common causes
- Right-sided heart failure: from heart disease, heartworm disease, or fluid around the heart.
- Liver disease: such as cirrhosis, which raises pressure in the liver’s blood vessels and lowers blood protein.
- Low blood protein (albumin): from protein-losing kidney disease or protein-losing gut disease.
- Cancer in the abdomen.
- Bleeding into the abdomen: from tumors, trauma, or rat poison.
- Urine leaking from a ruptured bladder after trauma.
- Peritonitis: infection or inflammation of the abdominal lining.
How vets diagnose it
- Ultrasound to confirm fluid and look at organs
- Abdominocentesis: removing a small fluid sample with a needle. The type of fluid (clear, bloody, cloudy) is one of the most useful clues.
- Bloodwork and urine tests, including protein levels and liver and kidney values
- Chest X-rays, heart ultrasound, and heartworm testing
- Clotting tests if bleeding is suspected
Treatment
- Treat the underlying cause: heart medications, liver or kidney treatment, surgery for bleeding tumors, antibiotics for infections, or vitamin K1 for anticoagulant rat poison.
- Diuretics such as furosemide or spironolactone, for heart or liver causes.
- Draining fluid if the belly is so full it makes breathing hard. This gives relief but fluid often returns until the cause is controlled.
- Diet changes, such as sodium restriction or a specific liver, kidney, or gut diet, as your vet advises.
Home care
- Give medications exactly as prescribed, and don’t stop diuretics without your vet.
- Count breathing at rest: your vet can tell you what’s normal for your dog. Call if it rises.
- Weigh regularly and watch belly size.
- Keep fresh water available, since diuretics increase thirst and urination, and allow frequent bathroom breaks.
- Avoid salty treats and table scraps.
- Gentle activity only, as advised.
What to avoid
- Human diuretics or “water pills,” which can cause dangerous dehydration and electrolyte problems.
- Herbal “detox” or liver products without vet approval.
- Restricting water to reduce fluid, which doesn’t work and can harm your dog.
- Assuming a big belly is just weight gain, especially if it came on over days or weeks.
Frequently asked questions
Can ascites in dogs be cured?
It depends on the cause. Fluid from a treatable problem, such as rat poison or some infections, can resolve completely. Fluid from heart or liver disease can often be controlled for a long time with medication.
Is draining the fluid enough?
No. Draining relieves pressure, but the fluid returns unless the cause is treated.
Is ascites painful for dogs?
A large amount of fluid is uncomfortable and can make breathing hard. Treatment usually makes dogs much more comfortable.
Sources
- Merck Veterinary Manual: Ascites in small animals
- Merck Veterinary Manual: Heart failure in dogs
- American Heartworm Society: Canine heartworm guidelines
- Merck Veterinary Manual: Hemoabdomen and splenic tumors in dogs
This article is for general education and is not a substitute for care from your own veterinarian. Learn about The Pet Vet and our editorial policy.