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Pleural effusion in cats
Pleural effusion is the accumulation of fluid in the space between the lungs and the chest wall. This liquid takes up the space that the lungs need to fill with air: they can no longer expand, and the cat gradually suffocates. It is not a d...
What is it?
Pleural effusion is the accumulation of fluid in the space between the lungs and the chest wall. This liquid takes up the space that the lungs need to fill with air: they can no longer expand, and the cat gradually suffocates.
It is not a disease in itself, but the visible consequence of another condition: heart disease, infection, tumor, feline infectious peritonitis, accident.
Two things must be remembered. First of all, it is an absolute life-threatening emergency. Then, the cat hides its discomfort for a very long time: when the signs become obvious to the owner, the situation is already advanced.
Key point
Absolute life-threatening emergency. A cat that breathes with its mouth open or whose belly pumps while resting can die within minutes if stressed or strained. What to do: call the clinic to notify you of your arrival, place the cat in a transport box open on the top, without forcing it or turning it over, avoid noise and heat, and drive straight away. Do not try any treatments at home.
Commonly observed signs
These signs are neither exhaustive nor specific. Only a veterinarian can establish a diagnosis.
Related signs — each one links to its page:
Rapid, shallow breathing at rest, with marked movement of the stomach.
Cat which remains seated or lying on its stomach, elbows apart, head and neck stretched forward, and which refuses to lie on its side.
Open mouth breathing: in cats, this sign is always serious.
Deep depression, refusal to move, to eat, to play.
Pale, gray or bluish gums.
Fever when the effusion is due to an infection.
Cough is rare, contrary to what one would expect from a respiratory problem.
When to consult without delay
This list does not replace veterinary advice. It gathers situations that justify a prompt consultation.
Causes and risk factors
Heart failure: A poorly functioning heart allows fluid to build up in the chest. It is one of the most common causes in cats.
Pyothorax: accumulation of pus, often after a bite wound that has perforated the wall, or after a lung infection.
Feline infectious peritonitis, particularly in young cats.
Tumors of the chest, especially certain lymphomas that develop in front of the heart.
Chylothorax: accumulation of lymph, a whitish liquid, due to damage to the lymphatic vessels.
Trauma, including a fall or shock, with bleeding in the chest.
Known heart disease or murmur detected during a previous visit.
Outgoing Cat Fighting: Deep bites to the chest wall can lead to pyothorax.
Young cat from a community, for feline infectious peritonitis.
Elderly cat, for tumor causes.
Public road accident or fall from a balcony.
Current lower respiratory infection.
Diagnosis and care
Diagnosis is the veterinarian's responsibility, based on clinical examination and laboratory tests. Care is decided case by case.
The priority is not diagnosis but stabilization: a cat in respiratory distress is placed on oxygen and handled as little as possible. Forcing such a cat to examine it may be enough to cause a shutdown.
The chest ultrasound, carried out without having to lay the cat down, shows the fluid quickly and without stress.
The veterinarian then removes part of the liquid by a puncture: this action provides immediate relief and provides the sample to be analyzed.
The appearance and analysis of the fluid strongly point towards the cause: pus, blood, lymph, feline infectious peritonitis fluid, tumor cells.
X-rays, an ultrasound of the heart and a blood test complete the assessment once the cat is stabilized.
Treatment
The first action is the evacuation of the liquid and the supply of oxygen: the cat breathes again almost immediately.
Basic treatment depends entirely on the identified cause: cardiac medications in the event of heart failure, prolonged antibiotic therapy and drainage in the case of pyothorax, specific treatment for feline infectious peritonitis, protocol adapted for a tumor.
A chest drain is sometimes placed to empty the chest several times a day, particularly in the event of pus: this requires hospitalization.
No home treatment can replace the evacuation of the fluid. Do not try to make your cat breathe yourself, do not give him any human medication: many are fatal for him.
Close monitoring is necessary because the fluid can reform.
Treatment depends on the cause and the animal's condition: it must be determined by a veterinarian. No self-medication.
Prevention
We prevent the causes, not the effusion itself.
Have the cat's heart examined at each annual visit; a murmur detected early allows cardiac monitoring before the attack.
Sterilize and limit fighting, to reduce the risk of penetrating chest wounds.
Have any bite wound examined immediately: a small closed wound can harbor a deep infection.
Secure balconies and windows.
Monitor the resting respiratory rate in a cat known to have a heart condition: this is the earliest warning indicator, and the veterinarian can teach you how to measure it.
Possible complications
Respiratory arrest due to lack of oxygen, including during excessive handling of the cat.
Rapid recurrence of fluid until the cause is treated.
Spread of an infection throughout the body in case of pyothorax.
Scars and adhesions between the lung and the wall after an old infection, which permanently limit breathing.
When to see a veterinarian
Your cat is breathing with its mouth open: go to a veterinarian immediately, without any further steps.
His breathing is rapid and his stomach pumps while he is at rest.
He refuses to lie on his side and remains seated with his neck stretched.
Its gums are gray or bluish.
He is brutally killed, no longer eats and hides.
He was bitten, fell or had an accident, even several days ago, and is breathing poorly today.
Prognosis
The prognosis depends almost entirely on the cause and the speed of treatment.
A pyothorax treated completely, with drainage and long-term antibiotic therapy, heals in a good number of cases.
An effusion of cardiac origin is controlled with lifelong treatment and regular monitoring, but indicates an already advanced disease.
Tumor causes and feline infectious peritonitis have a poorer prognosis, to be discussed on a case-by-case basis with the veterinarian.
In all cases, a cat evacuated and oxygenated in time has a much better chance than a cat brought in a few hours later.
Frequently asked questions
How do I know if my cat is breathing too fast?
When he is sleeping peacefully, count the movements of his chest for fifteen seconds, then multiply by four. Note this number when he is doing well: this is his reference value. A clear and lasting increase in this frequency, especially in a cat known to have a heart condition, should lead you to consult before the appearance of other signs.
My cat feels better immediately after the puncture: is he cured?
No. Removing the fluid relieves it immediately, but does not treat the cause. Without basic treatment, the liquid reforms, sometimes within a few days. The assessment following the puncture is therefore essential.
Why should you not handle a cat that is breathing poorly?
Because he is already at the limit of his abilities. Constraining him, turning him onto his back or holding him firmly may be enough to turn the situation around. Even in the clinic, the examination is deliberately kept to a minimum as long as the cat is not oxygenated.
Could an old bite be the cause?
Yes. A bite to the chest quickly closes on the surface while leaving bacteria deep down. A pyothorax can appear days or weeks later. This is why any bite wound in a cat should be shown to a veterinarian.
References
AAFP — American Association of Feline Practitioners
Content reviewed by the TunisieVet editorial team · Updated 09 August 2026
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