Heart Disease and Murmurs in Dogs and Cats: A Guide

Important: This article is general educational information and is not a substitute for an in-person veterinary examination. If your pet shows sudden difficulty breathing, collapse, or blue-tinged gums, treat it as an emergency and contact your veterinarian or an emergency clinic immediately.

The heart works quietly in the background, beating tens of thousands of times a day, so it is easy to overlook until something goes wrong. Heart disease is common in both dogs and cats, and many forms develop gradually with few obvious signs until the condition is advanced. Learning what a heart murmur means, which signs deserve attention, and how veterinary care can help will make you a better advocate for your pet's long-term health. This guide walks through the basics in plain language.

One theme runs throughout: many heart problems are far more manageable when caught early, which is one of the best arguments for regular veterinary check-ups even when your pet seems perfectly well.

A Quick Look at How the Heart Works

The heart is a muscular pump divided into four chambers, with valves that keep blood flowing in one direction. The right side sends blood to the lungs to pick up oxygen; the left side pumps oxygen-rich blood out to the body. When the muscle, the valves, or the heart's electrical system are not working properly, the pump becomes less efficient. The body tries to compensate, but over time these adjustments can lead to congestive heart failure, where fluid backs up into the lungs or abdomen.

Understanding this basic plumbing helps explain why heart disease can cause coughing, breathing trouble, exercise intolerance, and fluid build-up — they are downstream effects of a pump that is struggling.

What a Heart Murmur Means

A heart murmur is an extra sound the veterinarian hears through the stethoscope, caused by turbulent blood flow within the heart. Murmurs are graded by loudness, and your veterinarian may describe one on a scale from soft to very loud. It is important to understand what a murmur is and is not: a murmur is a finding, not a diagnosis. It tells your veterinarian to look more closely, not necessarily that your pet is seriously ill.

Some murmurs are harmless — for example, certain murmurs in young puppies and kittens may be innocent and resolve with growth. Others reflect underlying heart disease such as a leaky valve or a structural abnormality. Because a murmur cannot, on its own, reveal the full picture, your veterinarian may recommend further tests to understand its cause and significance.

Common Heart Conditions in Dogs

Dogs develop several recognizable heart conditions, and the likelihood varies with breed, age, and size:

• Degenerative valve disease: A very common condition, especially in older small-breed dogs, in which a heart valve thickens and leaks over time, often producing a murmur.
• Dilated cardiomyopathy: A disease in which the heart muscle becomes enlarged and weak, more often seen in certain larger breeds.
• Congenital defects: Some dogs are born with structural heart abnormalities that are detected early in life.

The course of these conditions varies widely. Some dogs live for years with a stable murmur and never develop symptoms, while others progress to heart failure and need ongoing treatment. Regular monitoring helps your veterinarian act at the right time.

Common Heart Conditions in Cats

Cats tend to hide heart disease exceptionally well, which makes feline heart conditions especially important to watch for. The most commonly recognized form is hypertrophic cardiomyopathy, in which the heart muscle walls thicken, reducing the heart's efficiency. Cats may show no outward signs for a long time, and sometimes the first indication of a problem is a sudden, serious event.

Two particularly concerning complications in cats are the development of blood clots, which can cause sudden pain and paralysis (often of the hind limbs), and the rapid onset of breathing difficulty from fluid in or around the lungs. Both are emergencies. Because cats so often lack early warning signs, veterinary examinations and any recommended screening are valuable, particularly as cats age.

Signs of Heart Trouble to Watch For

Signs can be subtle and develop slowly. Contact your veterinarian if you notice:

• Coughing (more typical in dogs than cats), especially at night or after lying down.
• Increased breathing rate or effort, including a rising resting respiratory rate.
• Tiring quickly, reluctance to exercise, or needing to rest during walks or play.
• Fainting or collapse, sometimes with excitement or exertion.
• A swollen belly, weight or appetite changes, or restlessness at night.
• In cats, sudden hind-limb weakness or pain, which is an emergency.

A practical home skill is counting your pet's resting or sleeping respiratory rate and learning what is normal for your individual animal. A steady upward trend or a sudden increase can be an early sign of fluid build-up and is worth reporting promptly.

How Veterinarians Diagnose Heart Disease

After hearing a murmur or noticing concerning signs, your veterinarian may recommend a combination of tests to clarify what is happening:

• Physical examination: Listening to the heart and lungs, checking pulses, gum color, and signs of fluid.
• Chest X-rays: To assess heart size and look for fluid in the lungs.
• Echocardiogram (heart ultrasound): A detailed look at the heart's structure and function, often the key test for understanding the specific disease.
• Electrocardiogram (ECG): To evaluate heart rhythm.
• Blood pressure and blood tests: To assess overall health and contributing factors.

Not every pet needs every test. Your veterinarian tailors the workup to your pet's situation, sometimes referring to a veterinary cardiologist for advanced evaluation.

Treatment and Ongoing Care

Treatment depends entirely on the specific diagnosis, the stage of disease, and your individual pet, and it must be directed by a veterinarian. In some early cases, monitoring alone is appropriate. In others, medications are prescribed to help the heart work more effectively, manage fluid build-up, or address rhythm problems. The aim is generally to support quality of life and slow progression, and many pets do well for a long time with the right plan.

If your pet is prescribed heart medication, give it exactly as directed and never stop abruptly without veterinary guidance. Keep all recheck appointments, since treatment often needs fine-tuning as the condition evolves. Report changes such as a rising resting respiratory rate, new coughing, reduced appetite, or decreased energy between visits.

A note on diet and supplements

Your veterinarian may make specific dietary recommendations as part of a heart-care plan; follow these rather than making changes on your own. Any supplement should be considered only as a possible complement to — never a substitute for — veterinary diagnosis and prescribed treatment, and should be discussed with your veterinarian first, because some can interact with medications. Never use a supplement, food, or product in place of professional cardiac care.

Living Well With a Heart Condition

Many pets with heart disease enjoy a good quality of life with thoughtful day-to-day care:

• Maintain a healthy weight: Excess weight makes the heart work harder; ask your veterinarian about an ideal body condition.
• Right-size exercise: Gentle, regular activity is usually encouraged, but follow your veterinarian's advice on limits.
• Monitor at home: Track resting respiratory rate and note any new signs.
• Reduce stress and overheating: Avoid strenuous activity in hot, humid weather.
• Stay consistent with medication and rechecks: Consistency is the backbone of good control.

Myths and Facts

Myth: A murmur always means my pet is dying. Fact: A murmur is a sound, not a diagnosis. Some are harmless; others need monitoring or treatment. Testing clarifies the meaning.

Myth: If my pet acts normal, the heart must be fine. Fact: Cats in particular hide heart disease, and dogs can compensate for a long time. Normal behavior does not rule out a problem.

Myth: Heart disease only affects old pets. Fact: While risk rises with age, congenital conditions and certain diseases can affect young animals too.

Myth: There is nothing that can be done. Fact: Many pets live comfortably for a long time with appropriate veterinary management.

Frequently Asked Questions

My vet heard a murmur but my dog seems fine. What now?

Your veterinarian will advise whether monitoring or further testing such as an echocardiogram is appropriate. Follow their recommendation, and watch for any new signs at home.

How do I count my pet's resting respiratory rate?

While your pet is calm or asleep, count each breath (one rise and fall of the chest) for 30 seconds and double it. Learn your pet's normal baseline so you can spot changes.

Can heart disease be cured?

Most chronic heart conditions are managed rather than cured, but management can be very effective at supporting comfort and quality of life. Your veterinarian will explain what to expect for your pet's specific diagnosis.

Is heart disease painful?

Many forms are not overtly painful, but complications such as a blood clot in cats can be very painful and are emergencies. Breathing distress is also distressing and needs urgent care.

The Bottom Line

Heart disease in dogs and cats is common, often silent in its early stages, and frequently very manageable when identified in time. A heart murmur is a clue that prompts closer evaluation rather than a verdict, and tests such as chest X-rays and an echocardiogram help reveal the underlying picture. Watch for coughing, increased breathing effort, exercise intolerance, fainting, a swollen belly, and — in cats — sudden hind-limb weakness, which is an emergency. Counting your pet's resting respiratory rate is a simple, powerful way to catch trouble early.

Because cats hide heart disease so well and dogs can compensate for a long time, normal behavior does not guarantee a healthy heart, which is why routine veterinary check-ups matter. When a diagnosis is made, work closely with your veterinarian, give medications exactly as prescribed, keep rechecks, and treat any diet or supplement decisions as part of the veterinary plan rather than a replacement for it. With early detection and steady care, many pets with heart conditions continue to thrive for years.