What early signs can an atrial septal defect cause in dogs and cats?

Early signs may be subtle, but common changes include rapid breathing, reduced exercise tolerance, reduced appetite, or weight changes. If your pet is less active or panting, book a veterinary check.

How does a vet confirm an atrial septal defect?

Diagnosis is mainly confirmed with echocardiography, which checks heart structure and abnormal blood flow. Chest X-rays and an ECG may also be used to assess heart function and complications.

Does finding a heart murmur always mean surgery is needed?

A heart murmur is a sign that further assessment is needed, but it does not always mean surgery is required. Whether catheter-based treatment or surgery is needed depends on test results and clinical signs.

What tests are needed for follow-up visits?

Common follow-up tests include echocardiography, chest X-rays, an ECG, and blood tests. The frequency depends on how stable your pet is and your vet's recommendation.

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

Atrial Septal Defect in Dogs and Cats: Breathing Difficulty, Echocardiography & Home Care [2025]

Atrial septal defect is a congenital heart disease. Mild cases may have no signs, while severe cases may need surgery or catheter-based treatment.

Take 1 minute to check the symptoms first

Last updated: 2026/01/05

PetHealthMap Editorial Team

Sources: ACVIM, WSAVA, National Taiwan University Veterinary Hospital

When to See a Vet

Seek emergency care immediately

•Persistent and obvious open-mouth breathing with rapid respiratory rate
•Sudden collapse or prolonged loss of consciousness with minimal responsiveness
•Noticeably blue or pale/white gums or tongue

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

•Markedly decreased activity level or easy fatigue and weakness
•Intermittent labored breathing at rest or after exercise
•Persistent abdominal distension or reduced appetite

01What symptoms may mean something is wrong?

Dogs and cats with an atrial septal defect may show breathing or circulation changes related to increased strain on the heart, and some signs need prompt attention.

Persistent or intermittent rapid breathing or open-mouth breathing
Fluid in the abdomen or obvious abdominal swelling with discomfort or reduced activity
Bluish gums or skin, or a change in colour, which may indicate low oxygen
Fainting or collapse after exercise or while resting
A heart murmur or irregular heart rhythm may be detected during a veterinary visit
If any of the above occur, arrange a veterinary assessment as soon as possible

Seek emergency care immediately if you notice the following symptoms:

⚠️ Seek veterinary care immediately for ongoing breathing difficulty or open-mouth breathing
⚠️ Go to an emergency vet straight away if your pet suddenly collapses or loses consciousness
⚠️ Seek urgent veterinary care if the gums or tongue look noticeably blue, purple, or pale

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

Home records and observations help your vet understand how the condition is changing and can speed up diagnosis and assessment.

Record the breathing rate per minute and whether breathing looks laboured
Watch and record changes in alertness and activity levels over time
Keep a daily record of appetite, water intake, urination, and bowel movements
Use scales to measure and note body weight trends
Take short videos of abnormal breathing or behaviour during activity
If you notice abnormalities, arrange a cardiology or general veterinary assessment promptly

03How will the vet diagnose it? Common tests

At the clinic, your vet will choose tests based on your pet's clinical signs to assess heart structure and function.

Physical examination

includes listening to the heart and lungs and assessing circulation

Chest X-rays

assess heart size, fluid in the lungs, or changes in blood vessels

Electrocardiogram (ECG)

checks heart rhythm and conduction abnormalities

Echocardiography

directly assesses the location of the septal defect and blood flow

Blood tests and biochemistry

assess overall organ function and concurrent disease

Urinalysis

helps assess kidney function and fluid status, which supports medication planning

CT or other advanced imaging may be arranged if needed to support assessment

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

Treatment depends on the size of the defect and clinical signs. Medication, surgery, or referral may all be considered, and ongoing monitoring and rechecks are important.

Medication plans require regular rechecks and adjustment based on your pet's condition
Diet changes and weight control can help reduce strain on the heart and related signs
Continue monitoring breathing and abdominal fluid changes, and tell your vet if they worsen
Have follow-up echocardiograms as advised to monitor changes in heart structure and function
Schedule rechecks and any necessary laboratory or imaging follow-up as recommended by your vet
Referral to a veterinary cardiologist or teaching hospital may be needed for further assessment

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

Record when signs first appeared, how often they happen, and the situation around each episode

Bring or prepare short video clips of breathing changes or fainting episodes

List recent changes in appetite, drinking, toileting, and activity level

Bring all current medications, supplements, and dosing records

Bring previous test reports or images, such as X-rays or ultrasound records

When booking by phone, describe the signs and ask whether any tests require preparation beforehand

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.