What are the common causes of pleural effusion?

Pleural effusion has many possible causes, including heart disease, infection, tumours, and trauma. The vet will use imaging and fluid analysis to identify the most likely cause and arrange the appropriate treatment. Follow your vet's advice for further investigation.

What should I do if I notice my pet breathing rapidly at home?

If your pet is breathing rapidly or experiencing difficulty breathing, seek veterinary attention or go to an emergency clinic as soon as possible. Keep your pet calm and avoid any strenuous activity before the visit. Have the time symptoms started and any video clips ready for the vet.

Is a chest tap (thoracocentesis) dangerous?

Thoracocentesis is a common procedure that can quickly relieve breathing difficulty. The risks and benefits should be assessed by your vet. The collected fluid is usually sent to a laboratory to help with diagnosis and guide ongoing treatment.

How long does treatment for pleural effusion require hospitalisation?

Whether hospitalisation is needed and for how long depends on the cause of the fluid and the severity of the condition. Mild cases may require only short-term observation, while more severe or complex cases may need several days of inpatient care. Follow your vet's recommendation.

How much do the tests and treatment for this condition usually cost?

Costs vary by clinic and region — ask your vet for an estimate before proceeding.

Disease Guide

Pleural Effusion in Dogs & Cats: Symptoms, Diagnosis & Treatment [2025]

Fluid in the chest cavity impairs breathing and requires prompt diagnosis to identify the underlying cause.

Take 1 minute to check the symptoms first

Last updated: 2026/01/06

Pethealthmap Editorial Team

Sources: ACVIM, WSAVA, National Taiwan University Veterinary Hospital

When to See a Vet

Seek emergency care immediately

•Persistent severe breathing difficulty that cannot be relieved
•Sudden obvious bluish-purple discoloration of the gums or lips
•Sudden fainting or brief loss of consciousness

Schedule a clinic visit soon (within 24–72 hours)

•Noticeably decreased activity level lasting more than one day
•Persistently faster breathing than usual
•Persistent or intermittent severe coughing

01What symptoms indicate something is wrong?

Pleural effusion impairs breathing and activity. Common signs include lethargy, coughing, and laboured breathing. Seek emergency care immediately if cyanosis or respiratory distress is present.

Lethargy, noticeably reduced activity, or reluctance to move
Persistent or intermittent severe coughing, or coughing up foam
Rapid breathing, wheezing, or a clearly increased respiratory rate
Open-mouth breathing or laboured exhalation; breathing appears effortful
Purple or bluish gums or lips (cyanosis), suggesting possible low blood oxygen

Seek emergency care immediately if you notice the following symptoms:

⚠️ Breathing difficulty or rapid breathing that does not improve
⚠️ Obvious purple or bluish discolouration of the gums or lips (cyanosis)
⚠️ Fainting or a brief loss of consciousness

02How should you assess the situation at home? Key observations and emergency criteria

Observing and recording symptom details at home helps the vet carry out an initial assessment and plan appropriate tests. If breathing difficulty is severe, go to an emergency clinic first.

Note the exact time symptoms started and how they have changed over time
Count the resting respiratory rate per minute (recording a video can help)
Use your phone to film short clips of the breathing, coughing, and activity levels
Track changes in appetite, water intake, and urination or defecation
Watch for coughing up blood, foam, or visible discharge from the nose or mouth

03How will the vet diagnose this? Common diagnostic tests

At the clinic the vet will use clinical examination and imaging to assess the volume of fluid and its likely cause. Fluid may be collected for laboratory analysis to guide further treatment.

Full physical examination

chest auscultation and palpation to assess breathing

Chest X-ray

to evaluate the location and volume of fluid and the degree of lung involvement

Cardiac ultrasound (echocardiography)

to check whether a heart condition is contributing to fluid accumulation

Thoracocentesis (chest tap)

to relieve breathing difficulty and analyse the fluid

Fluid cytology and bacterial culture to look for evidence of infection or tumour

CT scan or other advanced imaging and specialist referral if indicated

04How is it treated and managed after diagnosis? Medications, diet, and care guide

Treatment focuses on improving breathing and addressing the underlying cause. Regular imaging follow-up and clinical monitoring are required after discharge, with medications adjusted and a rehabilitation plan arranged per the vet's instructions.

In acute cases, thoracocentesis can be performed first to relieve breathing difficulty and monitor the response
Targeted or supportive treatment is given based on fluid analysis results
Medications and procedures must be adjusted at scheduled follow-up visits as directed by the vet
After discharge, monitor diet, rest, and avoid strenuous activity
Routine X-ray or ultrasound follow-up to track fluid changes and treatment effectiveness
Referral to a specialist hospital is recommended for complex cases or suspected tumour or heart disease

05What should you prepare before the appointment? Key information to help the vet identify the cause quickly

Record when symptoms started, how often they occur, and any daily changes

List all current medications, supplements, and known allergies

Bring videos or photos of breathing, coughing, or activity for reference

Note recent changes in appetite, water intake, and urination or defecation

Bring any previous chest X-rays or ultrasound reports if available

If breathing difficulty is present, go to an emergency clinic first, then arrange a follow-up consultation

This content is for reference only and cannot replace a professional veterinary diagnosis. If your pet shows signs of illness, please seek veterinary care promptly.