What are the common causes of myocarditis in dogs and cats?

Myocarditis is commonly caused by infection (such as bacterial or viral), immune-mediated reactions, or toxins, but the exact cause must be confirmed through laboratory tests and imaging — consult your vet for further evaluation.

What tests does the vet use to diagnose myocarditis?

Common tests include blood work and biochemistry, an ECG, cardiac ultrasound (echocardiography), and chest X-ray; pathogen testing or specialist referral may also be required to identify the cause.

Does treatment for myocarditis require hospitalisation?

Whether hospitalisation is needed depends on the severity of symptoms; pets with breathing difficulty or haemodynamic instability may require inpatient monitoring, while milder cases may be managed with outpatient follow-up — always follow your vet's recommendation.

What follow-up tests are needed after treatment?

Follow-up typically includes echocardiography, ECG, and blood tests to monitor cardiac function and treatment response; the frequency of revisits is adjusted based on the condition and your vet's advice.

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

Myocarditis in Dogs & Cats: Symptoms, Diagnosis & Home Care [2025]

Myocarditis is inflammation of the heart muscle that can be caused by infection, immune reactions, or toxins, leading to arrhythmias and reduced cardiac function.

Take 1 minute to check the symptoms first

Last updated: 2025/12/16

PetHealthMap Editorial Team

Sources: ACVIM, WSAVA, Taiwan Veterinary Internal Medicine Society

When to See a Vet

Seek immediate veterinary care (emergency)

•Persistent difficulty breathing with open-mouth panting and inability to perform any activity
•Repeated or prolonged fainting or loss of consciousness
•Blue or purple discoloration of the lips or gums with cold extremities

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

•Noticeably reduced activity level lasting more than two days
•Frequent coughing or clearly abnormal breathing sounds
•Irregular heartbeat (too fast or too slow) or a palpable heart palpitation

01What symptoms indicate something is wrong?

Myocarditis affects the heart's ability to contract and conduct electrical signals, often causing reduced activity levels and breathing-related symptoms in dogs and cats.

Persistent weakness or noticeably reduced activity — unwilling to play or go for walks
Recurring or intermittent fever, with body temperature higher than normal
Prolonged or frequent coughing, or a change in the character or frequency of the cough
Rapid breathing, open-mouth breathing, or signs of laboured respiration
Sudden collapse, brief loss of balance, or falling to the ground
Irregular heart rhythm, with palpitations or abnormal heartbeat sensations
If any of the above signs appear, it is advisable to arrange a clinic evaluation as soon as possible

Seek emergency care immediately if you notice the following symptoms:

⚠️ Breathing difficulty or rapid breathing that does not improve
⚠️ Collapse or brief loss of consciousness
⚠️ Gums or lips turning blue or pale

02How can you assess the situation at home? Key observations and criteria for seeking emergency care

Systematically recording symptoms and physical changes at home helps the vet quickly understand how the condition is progressing and prioritise the appropriate investigations.

Measure and record body temperature daily, noting any upward or downward trends
Log the number of coughing episodes, the time of day they occur, and their severity
Observe and note the breathing rate and effort during rest and activity
Record mental alertness, changes in energy level, and behaviour at rest
Monitor for noticeable changes in appetite, water intake, and body weight
Note whether the frequency and appearance of urination and defecation are abnormal
If possible, record video or audio of symptoms and bring it to the appointment for the vet's reference

03How will the vet make a diagnosis? Common examination steps

After arrival, the vet will combine clinical examination with imaging and laboratory tests to identify the likely cause and assess severity.

Physical examination

full cardiopulmonary auscultation along with pulse and capillary refill time assessment

Blood tests

complete blood count, inflammatory markers, and organ function assessment

Biochemistry and urinalysis

to assess whether organs such as the liver and kidneys are affected

Pathogen screening or bacterial/viral testing to identify the underlying cause

Electrocardiogram (ECG)

to evaluate arrhythmias and electrophysiological abnormalities

Cardiac ultrasound (echocardiography)

to assess myocardial structure and contractile function

Chest X-ray or CT imaging

to evaluate heart size and pulmonary changes

If needed, referral to a specialist hospital with cardiac diagnostic capabilities is recommended for further evaluation

04What treatment and care are needed after diagnosis? Medications, dietary adjustments, and care guide

Treatment for myocarditis must be tailored to the underlying cause and severity; following treatment, ongoing medication management and regular monitoring are essential to track progress.

Start or adjust medications as directed by your vet and follow the scheduled follow-up plan
Schedule regular echocardiography or ECG to confirm the response to treatment
Regular blood and biochemistry tests to assess overall organ status
Restrict strenuous activity and maintain a calm environment to prevent overexcitement
Continue monitoring breathing, alertness, and elimination patterns at home
Discuss long-term monitoring, prognosis, and care considerations with a specialist hospital

05What should you prepare before seeing the vet? Key information to help the vet quickly identify the cause

Record when symptoms first appeared, how they have progressed, and a timeline of frequency

List all current medications, supplements, and recent vaccination history

Bring recent records or videos of temperature readings, coughing episodes, and breathing patterns

Bring any previous test reports, X-rays, or ultrasound images if available

Note specific changes in appetite, water consumption, and elimination habits

Research and book an appointment in advance at a clinic or hospital with cardiac diagnostic capabilities

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.