What are the common symptoms of tetralogy of Fallot?

Common signs include cyanosis (blue-tinged gums or lips), reduced activity, repeated fainting, and poor growth. If your pet has breathing difficulty or faints, seek veterinary care as soon as possible.

What tests will the vet perform to confirm the condition?

Common tests include a physical examination, echocardiography, blood biochemistry, and urinalysis. CT or other advanced imaging may be recommended when needed to assess structural abnormalities.

What can I monitor at home to help the vet make a diagnosis?

You can record activity level, appetite, water intake, toileting, and weight changes, and take videos of breathing changes or fainting episodes for your vet to review.

If my pet's gums look blue, should I go to emergency care immediately?

If the gums are clearly blue or this occurs with breathing difficulty or fainting, go to an emergency vet immediately. If there is only a mild colour change, arrange a specialist appointment as soon as possible.

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

Tetralogy of Fallot in Dogs and Cats: Cyanosis, Weakness, Echocardiography & Care [2025]

A congenital four-part heart defect causing cyanosis and low oxygen levels

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 immediate veterinary care (emergency)

•Sudden collapse or prolonged loss of consciousness
•Gums or lips that are clearly cyanotic or purple
•Persistent difficulty breathing or obvious rapid breathing

Schedule a clinic visit as soon as possible (within 24-72 hours)

•Persistently and noticeably reduced activity level with easy fatigue
•Repeated fainting or frequent sudden falls without warning
•Slow growth or persistent inability to gain weight

01What symptoms suggest something is wrong?

Tetralogy of Fallot is a congenital heart malformation that often causes low blood oxygen and altered blood flow, leading to clinical signs such as cyanosis, fatigue, and poor growth.

Markedly reduced activity levels and tiring easily
Blue or purple-tinged gums or lips (cyanosis)
Repeated fainting episodes or sudden collapse without warning
A heart murmur or abnormal heartbeat may be heard during a veterinary visit
Poor growth or failure to gain weight normally

Seek emergency care immediately if you notice the following symptoms:

⚠️ Sudden coma or prolonged loss of consciousness
⚠️ Clearly blue or purple gums or lips
⚠️ Ongoing breathing difficulty or clearly rapid breathing

02How can you assess abnormalities at home? Key observations and emergency warning signs

Observing and recording day-to-day changes at home helps your vet understand the disease course and plan appropriate tests.

Record when changes in alertness and activity level occur and how often
Write down any daily changes in appetite and water intake
Keep detailed notes on toileting frequency, colour, and stool or urine characteristics
Weigh your pet regularly and record the trend for at least one week
Use your phone to record breathing changes or fainting episodes when they happen

03How will the vet diagnose it? Common tests

Your vet will combine a physical examination with imaging and blood tests to assess structural abnormalities and overall metabolic status.

Physical examination

including auscultation, palpation, and assessment of vital signs

Echocardiography

assesses heart structure and blood flow dynamics

Advanced imaging (CT) may be used for complex anatomy or surgical assessment

Blood tests and biochemistry

evaluate oxygenation and organ function

Urinalysis

helps rule out metabolic or complication-related problems

04How is it treated and managed after diagnosis? Medication, diet adjustments, and care guidance

Treatment aims to improve oxygenation, control symptoms, and monitor heart changes with imaging. An individualised follow-up plan is important.

Medication or surgery is decided after assessment by a specialist
Diet and weight management can help reduce the workload on the heart
Avoid strenuous activity and strong emotional stress at home
Attend regular follow-up visits and repeat echocardiography as advised
Assess the long-term outlook and adjust the follow-up schedule as needed

05What should you prepare before seeing the vet? Key details that help clarify the cause

Write down when the symptoms started, how often they occur, and how they have changed

Bring daily records of food intake, water intake, and toileting

Organise videos of fainting, panting, or abnormal breathing episodes

Bring all current medications, supplements, and previous test reports

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.