Can first-degree AV block in dogs and cats worsen quickly?

First-degree AV block is usually a mild delay in electrical conduction, and it does not always worsen quickly. However, if your pet faints, breathes rapidly, or suddenly becomes much less active, seek veterinary care immediately so your vet can assess the condition with an ECG and other tests.

What tests are usually done at the clinic?

Common tests include a physical examination, electrocardiogram (ECG), chest X-rays, and blood biochemistry. If needed, your vet may also recommend echocardiography or other advanced imaging.

Does my pet need immediate treatment if there are no symptoms?

If there are no clinical signs, your vet may recommend regular follow-up and ECG monitoring. Whether treatment is needed depends on the test results and clinical signs, so discuss the monitoring plan with your vet.

What information should I prepare for the consultation?

Bring records of when signs started and how they have changed, a list of medications and supplements, relevant test reports, and videos of fainting or abnormal gait. This information helps your vet assess the case quickly and plan the next tests.

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

First-Degree AV Block in Dogs and Cats: Weakness, Fainting, ECG Checks & Follow-Up Care [2025]

First-degree AV block is usually harmless and may be a normal variation linked to high vagal tone, but underlying problems still need to be ruled out.

Take 1 minute to check the symptoms first

Last updated: 2026/01/05

Pethealthmap Editorial Team

Sources: ACVIM, AAHA, National Taiwan University School of Veterinary Medicine, Taiwan Society of Veterinary Internal Medicine

When to See a Vet

Seek Immediate Veterinary Care (Emergency)

•Repeated fainting or multiple brief losses of consciousness
•Severe rapid breathing or obvious open-mouth breathing
•Extreme weakness with inability to stand up or move without assistance

Schedule a Veterinary Visit Soon (Within 24-72 Hours)

•Persistent or intermittent weakness
•Marked decrease in appetite with continued refusal to eat
•Repeated vomiting or diarrhea with increasing frequency

01What signs suggest something is wrong?

First-degree AV block in dogs and cats is common but may not be obvious, and is often noticed as reduced activity or intermittent weakness.

Persistent or intermittent weakness, with reduced activity levels
Reduced appetite or eating less than usual
Repeated vomiting or diarrhoea; record the number of episodes and timing
Lethargy or reduced interest in play and interaction
If these signs appear, arrange a veterinary consultation as soon as possible

Seek emergency care immediately if you notice the following symptoms:

⚠️ Repeated fainting or brief loss of consciousness
⚠️ Severe rapid breathing or worsening open-mouth breathing
⚠️ Extreme weakness, unable to stand or move without help

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

Before the appointment, you can record key information at home to help your vet understand how the condition is changing and what may be causing it.

Record when signs started, how often they occur, and whether they are changing
Monitor activity level, ability to stand, and walking pattern each day
Track daily food and water intake, plus episodes of vomiting or diarrhoea
Watch for changes in stool pattern or urine volume
Use your phone to record fainting episodes, abnormal gait, or breathing changes
Bring all records and videos to the consultation to help your vet assess the case

03How will the vet diagnose it? Common tests

At the clinic, your vet will start with a physical examination, then use ECG, imaging, or blood tests to identify the cause and severity.

Physical examination

listening to heart sounds and comparing pulse with heart rate

Electrocardiogram (ECG)

checking conduction delay and heart rhythm

Chest X-rays

assessing heart size and lung changes

Blood tests and biochemistry

screening for metabolic or infectious causes

Urinalysis and, when needed, advanced imaging such as echocardiography

04What treatment and care are needed after diagnosis? Medication, diet changes, and home care

Treatment and follow-up depend on clinical signs and test results. Pets without symptoms may be monitored, while pets with obvious signs need more active management and follow-up.

Pets without symptoms may only need regular follow-up and ECG monitoring
Pets with obvious signs may need hospital observation and further testing
Your vet will decide whether medication and a follow-up plan are needed based on the results
Adjust diet and activity to reduce overexertion and cardiac workload
Attend regular rechecks for ECG, blood biochemistry, and clinical assessment

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

Write down when signs began, how often they occur, and how they have changed

List all current medications, health products, and supplements

Bring videos of fainting, abnormal gait, or unusual breathing

Bring recent test reports, such as X-rays, ECGs, or blood tests

Consider booking a cardiology appointment by phone to reduce waiting time

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.