Holter Monitor (24-Hour ECG)

HeartQ&AMeongsiljang Veterinary Advisory Board

We’ve compiled everything you need to know about Holter monitor (24-hour ECG) testing for dogs and cats, including when it’s necessary, how the procedure is performed, costs, how to interpret the results, and precautions for pet owners.

What Is a Holter Monitor?

A puppy having some chest fur shaved and ECG electrodes attached.

A Holter monitor is a portable electrocardiogram device that continuously records your dog’s or cat’s heart rhythm for 24 hours or more. Its real value lies in capturing transient arrhythmias that appear and disappear within brief moments. It can help identify the cause of intermittent fainting, coughing, or lethargy—symptoms that are often missed by a standard 5-minute ECG performed in the clinic. If your pet experiences unexplained, recurrent fainting episodes, this test should definitely be considered.

When Is a Holter Test Necessary?

This is the first thing to consider when a dog experiences recurrent fainting of unknown cause, sudden collapse, or episodes of falling down after exercise. It’s also useful when an arrhythmia is suspected on a standard ECG but the diagnosis remains inconclusive, or when you want to confirm the effectiveness of heart medication. For breeds at high risk of dilated cardiomyopathy (DCM), such as Doberman Pinschers, or those prone to arrhythmogenic right ventricular cardiomyopathy (ARVC), like Boxers, screening is often recommended even in the absence of symptoms.

Standard ECG vs. Holter Monitor: What’s the Difference?

Item	Standard Electrocardiogram (ECG)	Holter Monitor
Recording time	1–5 minutes	24–48 hours
Diagnosis of intermittent arrhythmia	Difficult	Possible
Recording during daily activity	Not possible	Possible
Test location	Hospital	Home
Cost range (reference)	KRW 20,000–50,000	KRW 150,000–400,000

Cost may vary depending on the hospital and recording duration.

How Is the Test Performed?

We shave a small patch of chest fur and attach three to five electrode patches to the skin, then secure a small recording device inside a vest-style holder on your pet’s body. The setup usually takes 20 to 30 minutes and doesn’t require anesthesia. For the next 24 to 48 hours, your pet can go about their normal routine at home while the device continuously records heart activity. Once the monitoring period is over, you’ll return to the clinic to return the equipment, and our veterinarian will analyze the data using specialized software.

A dog comfortably resting at home, wearing a vest with a halter-mounted activity tracker.

Precautions to Follow During the Test

Water must never come into contact with the device. Bathing and swimming are prohibited, and walks should be avoided on rainy days. In some cases, an Elizabethan collar may be used to prevent your pet from chewing off the vest or electrodes. If an electrode becomes detached, data recording stops immediately, which may require restarting the test from the beginning. Contact the clinic right away if you notice the vest is loose or an electrode has come off.

How Are the Results Interpreted?

The veterinarian analyzes hundreds of thousands of heartbeats recorded over a 24-hour period using specialized software. - Number of ventricular premature contractions (VPCs): The total count per day. - Maximum and minimum heart rates: To identify extreme values. - Arrhythmia patterns: The specific forms in which they appear. - Heart rate variability: An indicator of autonomic nervous system balance. For example, in Doberman Pinschers, the frequency and morphology of VPCs serve as key indicators for diagnosing dilated cardiomyopathy. The veterinarian makes a comprehensive clinical judgment, considering clinical signs, to determine at what level these findings become clinically significant. The treatment plan is then determined based on how frequently and in what form the arrhythmias occur.

A veterinarian who analyzes electrocardiogram waveforms around the clock using a monitor

What Pet Owners Should Do During the Test

- Keep a symptom diary: Record the exact times your pet coughs, nearly collapses, or becomes agitated. - Log daily routines: Note down sleep, meal, walk, and play times. - Maintain normal activity: Avoid intentionally increasing or restricting exercise; keep to your usual routine. This helps the veterinarian correlate specific activities with arrhythmia episodes, significantly improving diagnostic accuracy.

Breeds Recommended for Testing Even Without Symptoms

- Doberman Pinscher: Early screening for dilated cardiomyopathy is recommended. - Boxer: At risk for arrhythmogenic right ventricular cardiomyopathy. - Irish Wolfhound and Great Dane: These large breeds are known to have a high incidence of heart disease, so regular cardiac check-ups are advisable. - Maine Coon and Ragdoll: These cat breeds are known to be susceptible to hypertrophic cardiomyopathy. Regular check-ups are especially recommended if there is a family history. Because significant heart damage may already be present by the time symptoms appear in these breeds, it is crucial to detect abnormalities early through screening while they are still asymptomatic and begin management promptly.

Reviewed by a veterinarian

Dr. Tony — Punnawat Phongkittirak

Veterinarian

A veterinarian who majored in veterinary medicine at Khon Kaen University, Thailand, and completed the IVSA program at North Carolina State University in the United States. Drawing on clinical experience at animal hospitals, he works in the pet healthcare field and is dedicated to building a digital care environment that connects pet parents with veterinarians.

Frequently Asked Questions

Is it okay for my pet to run and play as usual while wearing a Holter monitor?

Yes, regular walks and play are fine. However, swimming and vigorous water activities are prohibited, and please wait until after the examination to bathe your pet. Rather than trying to keep them unusually calm, maintaining their usual routine is more helpful for an accurate diagnosis.

How much does the test cost?

The cost varies depending on the clinic and the time of the test. Generally, a 24-hour test ranges from $100 to $300. Since analysis and interpretation fees may be charged separately, it's a good idea to confirm this when making your appointment.

When will the results be available?

It usually takes about 3 to 7 days after the device is returned. This is because we need time for our veterinary specialists and specialized software to carefully review hundreds of thousands of heartbeats.

Why isn't a standard ECG enough?

Standard ECGs only record for 1–5 minutes. If an arrhythmia occurs only a few times a day, the chance of catching it during a brief hospital visit is very low. A Holter monitor records continuously for 24 hours, so it won’t miss intermittent abnormalities.

Can cats undergo Holter monitoring?

It’s possible, but not easy. Cats often find vests uncomfortable and tend to try removing the device, so short-term event recorders or inpatient telemetry ECGs are commonly used as alternatives. Consult your veterinarian to choose the best approach for your cat.

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References

[1] Ettinger SJ, Feldman EC, Côté E, Textbook of Veterinary Internal Medicine, 8th Ed, Chapter 248 Electrocardiography

[2] Fox PR, Sisson D, Moïse NS, Textbook of Canine and Feline Cardiology: Principles and Clinical Practice, 2nd Ed

[3] Nelson RW, Couto CG, Small Animal Internal Medicine, 6th Ed, Cardiovascular System Chapter