What is sick sinus syndrome?

Sick sinus syndrome is a type of abnormal heart rhythm. It can cause brief weakness, fainting, or an abnormal pulse, and should be assessed with tests such as an ECG before you discuss next steps with your vet.

What should I do if my pet faints?

Keep the environment quiet, avoid moving an injured pet, record the episode time, and take a video if you can. If consciousness does not return or episodes recur, seek veterinary care immediately and bring your observation notes.

What main tests will be done at the clinic?

Common tests include an ECG, echocardiography, and blood biochemistry. Chest imaging or further monitoring may be arranged if needed to identify triggers or other conditions.

How long will follow-up be needed after treatment?

Depending on the condition, follow-up is usually needed over several weeks to several months, including ECG or ultrasound checks to assess treatment response. Follow your vet's advice on the exact recheck schedule.

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

Sick Sinus Syndrome in Dogs and Cats: Weakness, Fainting, ECG Tests & Care [2025]

An abnormal sinoatrial node can cause the heart rate to slow or pause

Take 1 minute to check the symptoms first

Last updated: 2026/01/06

Pethealthmap Editorial Team

Sources: ACVIM, AVMA, National Taiwan University Veterinary Hospital

When to See a Vet

Seek Immediate Veterinary Care (Emergency)

•Cannot be awakened and consciousness does not return
•Repeated seizure episodes that do not stop
•Suddenly collapses and cannot stand up or respond

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

•Brief loss of consciousness with recovery within a short time
•Repeated weakness or a marked decrease in activity
•Abnormal mentation or a marked decrease in appetite after an episode

01What symptoms suggest something is wrong?

Sick sinus syndrome often appears as sudden or repeated weakness, brief loss of consciousness, or episodic muscle twitching. Signs may be short-lived but can recur.

Persistent or intermittent weakness and reduced activity
Brief loss of consciousness or sudden fainting, often after excitement or exercise
Repeated or intermittent fainting episodes or brief periods of unresponsiveness
Seizure-like episodes or involuntary muscle tremors, seen as whole-body or localised twitching
May also have reduced appetite, changes in drinking, or low energy

Seek emergency care immediately if you notice the following symptoms:

⚠️ Cannot be woken and consciousness does not return
⚠️ Repeated seizure-like episodes that do not stop
⚠️ Suddenly collapses and cannot stand or respond

02How can I assess changes at home? Observation tips and emergency warning signs

Before visiting the clinic, observing and recording these details can help your vet understand the episode pattern and frequency, and may speed up diagnosis and treatment planning.

Record your pet's alertness and any changes in response to sound or touch
Write down when signs started, how often episodes occur, and how long they last
Track changes in appetite, water intake, urination, and bowel movements
Weigh your pet and note any recent trend in body weight
Use your phone to record episodes or unusual behaviour, including before and after the event
Bring these notes and videos to the vet visit for reference

03How will the vet diagnose it? Common tests

Clinic tests usually focus on assessing heart rhythm, heart structure, and overall health. If needed, your pet may be referred to a hospital with specialist equipment for further testing.

Physical examination

assesses alertness, pulse, heart and lung function, and peripheral circulation

Electrocardiogram (ECG)

assesses heart rhythm and conduction abnormalities

Echocardiography

checks heart structure and contraction function

Blood tests and biochemistry

help rule out metabolic or internal medical triggers

Chest imaging (X-ray or CT)

used to assess the lungs or heart size

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

After treatment, care usually centres on monitoring, medication adjustment, and regular follow-up. Depending on the situation, hospital observation or cardiology rechecks may be recommended.

Hospital monitoring may be arranged when needed to track vital signs and heart rhythm changes
Medication and dose adjustments should follow your vet's instructions and require follow-up visits
Diet and weight control can help reduce cardiac workload and support stability
At-home care should include a quiet environment and close monitoring for changes in signs
Regular rechecks may include ECG or ultrasound monitoring to assess treatment response
If signs worsen or change, arrange a cardiology assessment as soon as possible

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

Write down when signs began, how often episodes happen, and how long they last

List recent details of diet, water intake, urination, and bowel movements

Prepare videos or photos of episodes, including before and after the event

Bring a list of current medications, supplements, and doses

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

You may call ahead to book a cardiology appointment or tell reception the signs are urgent

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.