How is complete atrioventricular block diagnosed?

An electrocardiogram (ECG) is the main test used to confirm the heart rhythm and conduction block. Echocardiography and blood tests are often performed as well to check for related problems. Your vet can arrange a complete assessment.

Does fainting always mean my pet has a heart problem?

Not always. Fainting can be caused by heart rhythm problems, low blood sugar, neurological disease, and other issues. A vet needs to run tests to identify the likely cause and decide on the right management.

Does my pet need a cardiac rhythm device to improve?

Some patients are assessed for device implantation because their signs are severe, but whether it is needed depends on specialist assessment and test results. Follow your vet's advice.

How often are follow-up visits usually needed?

Follow-up frequency depends on the condition. Early on, visits may be every few weeks to a few months to monitor ECG and echocardiography changes. Please follow the schedule recommended by your vet.

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

Complete Atrioventricular Block in Dogs and Cats: Slow Heart Rate, ECG Diagnosis & Care [2025]

Complete atrioventricular block can cause a very slow heart rate and fainting, and many pets need a permanent pacemaker.

Take 1 minute to check the symptoms first

Last updated: 2026/01/05

Pethealthmap Editorial Team

Sources: ACVIM, AAHA, National Taiwan University Veterinary Hospital

When to See a Vet

Seek emergency care immediately

•Repeated or sustained loss of consciousness and collapse
•Noticeably blue or white lips or gums
•Extreme weakness — unable to stand or move on their own

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

•Noticeably reduced activity level lasting several days
•Rapid breathing or obvious fatigue during exercise
•Pulse or heart rate clearly much slower than normal

01What signs suggest something is wrong?

Complete atrioventricular block often causes the heart rate to become noticeably slow. Clinically, pets commonly show reduced activity or brief fainting episodes.

Lethargy and a clear drop in activity
Panting easily or tiring quickly during exercise or activity
A pulse or heart rate that is much slower than usual
Brief loss of consciousness or suddenly collapsing (fainting)
Reduced appetite and short-term weight loss

Seek emergency care immediately if you notice the following symptoms:

⚠️ Repeated or prolonged loss of consciousness with collapse
⚠️ Lips or gums that look clearly blue, purple, or pale
⚠️ Extreme weakness and being unable to stand or move without help

02How can I assess the problem at home? Observation points and when it may be an emergency

At home, you can observe and record changes. This information helps the vet assess severity and decide which tests should be prioritised.

Record when the signs first appeared, how often episodes happen, and how long they last
Track daily changes in appetite and water intake
Use your phone to take short videos of activity level, walking, and any fainting episode
Weigh your pet regularly and note any short-term changes
Watch whether urination and bowel movements are normal, including any change in frequency
Organise your notes and book an assessment at a clinic or hospital with cardiology equipment

03How will the vet diagnose it? Common tests

After arrival, the vet will assess heart function and overall health to confirm the source of the rhythm abnormality and check for any related problems.

Physical examination

listening to heart sounds, measuring blood pressure, and assessing overall condition

Electrocardiogram (ECG)

checks the heart rhythm and whether electrical conduction is interrupted

Echocardiography

assesses heart structure and pumping function

Blood tests and biochemistry

evaluates internal organ function and electrolyte status

Chest X-rays or advanced imaging, such as CT, if needed to assess related problems

Further testing at a clinic or hospital with cardiology equipment and specialist experience is recommended

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

Treatment and follow-up focus on stabilising the heart rhythm, improving signs, and long-term monitoring. Individualised care and regular check-ups are important.

Medication is considered by the vet when needed and adjusted according to the pet's condition
Some cases need assessment for the right timing of implanting a cardiac rhythm device
Regular follow-up visits to monitor changes on ECG and echocardiography
Home care includes plenty of rest and keeping a symptom diary
Adjust diet and activity level according to your vet's instructions
If signs worsen or episodes keep recurring, return to the vet immediately or seek specialist referral

05What should I prepare before seeing the vet? Key information that helps identify the cause

Write down the time, frequency, and duration of each episode

List all current medications and supplements

Bring recent ECG, ultrasound, or X-ray reports if available

Take videos or photos of recent fainting episodes or changes in activity

Record changes in eating, drinking, urination, and bowel movements

Call ahead to book with a cardiology specialist or a hospital with relevant equipment

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.

Related Symptoms (You May Also Be Looking For)

Bradycardia

Abnormally slow heart rate

Exercise Intolerance

Reduced exercise capacity

Jugular Distension

Distended jugular veins

Syncope

Fainting

Weakness

Reduced strength