What are the common causes of hemothorax?

Common causes include chest trauma (such as a road traffic accident), clotting disorders, and chest cavity tumours. A veterinary examination is needed to confirm the underlying cause.

What tests will the vet perform to confirm the diagnosis?

The vet will typically perform a physical examination, chest X-ray or ultrasound, and may perform thoracocentesis to analyse the fluid along with blood tests. A CT scan may be arranged if more detailed imaging is needed.

What signs at home indicate my pet needs immediate emergency care?

If you notice persistent difficulty breathing, sudden collapse, or blue or pale gums, take your pet to a veterinary emergency clinic immediately for professional assessment and treatment.

How much do the tests and treatment usually cost?

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

Disease Guide

Hemothorax in Dogs & Cats: Symptoms, Imaging & Acute Care Guide [2025]

Hemothorax — blood accumulating in the chest cavity — is a medical emergency commonly caused by trauma, clotting disorders, or tumours. Urgent thoracocentesis and identification of the bleeding source are required; severe cases may need blood transfusions.

Take 1 minute to check the symptoms first

Last updated: 2025/12/16

PetHealthMap editorial team

Sources: AVMA, AAHA, National Taiwan University Veterinary Hospital

When to See a Vet

Seek emergency care immediately

•Persistent open-mouth breathing with obvious respiratory distress
•Sudden collapse, weakness, or loss of consciousness
•Gums or oral mucosa appear purple or markedly pale

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

•Rapid breathing or intermittent panting with otherwise stable condition
•Noticeably reduced activity but still able to eat
•Frequent coughing or persistent dry cough

01What symptoms signal a problem?

Hemothorax (bleeding into the chest cavity) often causes noticeable changes in your pet's breathing and energy levels. Monitor your pet's breathing rate and activity closely.

Lethargy, noticeably reduced activity, or excessive sleepiness
Persistent or intermittent coughing with increased frequency
Rapid breathing, laboured breathing, or breathing with mouth open
Changes in gum or oral mucous membrane colour (pale or bluish)
If any of the above signs appear, arrange a veterinary evaluation promptly

Seek emergency care immediately if you notice the following symptoms:

⚠️ Obvious difficulty breathing or breathing with mouth open
⚠️ Sudden collapse, fainting, or loss of consciousness
⚠️ Blue or markedly pale gums

02How to assess the situation at home? Key observations and when to seek emergency care

Observing and recording changes at home provides your vet with valuable clues and helps speed up diagnosis.

Track coughing frequency, when episodes occur, and how long they last
Monitor alertness, activity levels, and exercise tolerance
Record any changes in appetite and water intake
Note changes in urination, bowel movements, and vomiting
Weigh your pet regularly and record weight trends
If symptoms worsen rapidly over a short period, seek veterinary care immediately

03How will the vet diagnose this? Common diagnostic tests

On arrival, the vet will begin with a physical examination and imaging. If needed, fluid may be collected from the chest cavity for further analysis.

Physical examination

assess breathing, heart rate, and circulatory status

Chest X-ray

evaluate fluid in the chest cavity, pneumothorax, or other abnormalities

Thoracic ultrasound or ultrasound-guided thoracocentesis (chest tap)

CT scan

provides more detailed imaging of the chest

Blood tests and biochemistry panel

assess anaemia, clotting function, and organ health

Specialist referral or further management may be recommended if needed

04How is hemothorax treated and managed? Medication, diet, and home care guide

Treatment includes acute intervention and ongoing follow-up. Your vet will arrange drainage, haemostasis, and supportive care based on your pet's condition.

Thoracocentesis or chest drain placement may be needed to relieve breathing difficulty and pressure
Pain relief, supportive care, and antimicrobial treatment as appropriate
Restrict vigorous activity and adjust diet to reduce strain
Schedule regular follow-up visits with imaging to monitor changes in the chest
Continue monitoring breathing, activity, and appetite at home and keep a record
Contact your specialist or clinic for a follow-up appointment if the condition fluctuates or worsens

05What to prepare before the vet visit? Key information to help the vet identify the cause quickly

Note when symptoms first appeared and how they have changed over time

Write down coughing frequency, breathing patterns, and energy levels

Record urination, bowel movements, vomiting, and appetite changes

Prepare a list of current medications and supplements

Bring short video clips or photos (coughing, breathing) to the consultation

If symptoms are urgent, call the clinic ahead of time to describe the situation

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.