Heart Murmurs in Cats: Symptoms, Treatment, & Life Expectancy

A diagnosis of a heart murmur in your cat can be worrying: this article aims to give you clear facts about what this means, and about the possible consequences for your cat’s health.

What Is a Heart Murmur?

Normally, when your DVM veterinarian listens to the sound of your cat’s heart with a stethoscope, they will hear a regular, healthy heart beat, which sounds a bit like the thump of one drum after another: it’s classically described as sounding like “lub dup” with the beating  sounding like “lub dup, lub dup, lub dup”, at a rate of around two or three “lub dups” every second.

A heart murmur is a swishing, whooshing, sound that the vet can hear with the stethoscope, as an extra noise, mixed up with the heart beat. Instead of “lubdup, lubdup”, the vet hears “lubshdup, lubshdup”, or “lubdubshhh, lubdupshhh”. It’s an abnormal sound which highlights that there is a potential problem that needs to be resolved.

What Causes a Heart Murmur?

This swishing, hissing sound of a heart murmur is caused by turbulent blood flow through or around the heart. If you imagine a wide, deep river flowing by, there’s no turbulence, and no noise. Now imagine a stream flowing  over rocks, or a river with rapids: the turbulence or disruption of the flow of the water creates a noise.

There are multiple common causes of the turbulent blood flow that leads to a heart murmur in a cat. Many causes are harmless, but some are serious and some are very serious indeed. The significance of a heart murmur depends on the cause of the murmur, and your veterinarian will analyse the murmur to work that out.

Heart Murmurs Are Classified in Different Ways

Loudness

Heart murmurs are graded on how easily they can be heard, on a scale of one to six, from quietest to loudest. The softest murmurs can be very hard to detect and may be only heard over one part of the heart. The loudest murmurs, suggesting more turbulence of the blood flow, can be heard over a wider area of the heart. Importantly, the significance of heart murmur does not depend just on the loudness: some quiet murmurs can indicate very serious disease, while some louder murmurs may be relatively benign.

The grading of heart murmurs is often somewhat subjective, and it’s based on the loudness of the murmur when the veterinarian listens to the chest with a stethoscope. The scale can be summarized as follows.

• Grade 1  – The faintest possible heart murmur: it may sometimes only be heard in the ideal situation, with a calm patient, in a quiet room, by a veterinarian with experience in listening to heart murmurs.
• Grade 2  – A quiet heart murmur that can be distinctly heard with a stethoscope, but not loud enough to cover up the normal sounds of the beating heart.
• Grade 3  – A moderately loud murmur that can be heard immediately when even an inexperienced veterinarian listens with a stethoscope, but still not loud enough to obscure the normal sounds of the beating heart.
• Grade 4 – A loud heart murmur that’s easily heard by an inexperienced veterinarian with a stethoscope and may begin to obscure the normal sounds of the beating heart.
• Grade 5  – A very loud heart murmur that obscures the normal sounds of the beating heart. It creates a physical vibration so that when a hand is placed on the cat’s chest, a “thrill” can be felt (this is a buzzy type of vibration caused by the loud murmur).
• Grade 6  – The loudest grade of heart murmur; can be heard even when the head of the stethoscope is held off the skin, away from physical contact with the chest.

Location

Your vet will identify where the heart murmur can be heard most distinctly: this can help to track down the underlying cause.

Nature

The dynamic nature of the heart murmur is important: is it constant, or does it change from heart beat to heart beat. Different terms are used to describe the murmur, such as galloping,

What Causes a Heart Murmur in Cats?

Structural Heart Disease Since Birth

Some cats have congenital heart defects i.e. they are born with an anatomical abnormality of the heart or of the blood vessels around the heart. Examples of an abnormal heart include ventricular septal defects (“holes in the heart”), pulmonic stenosis (narrowing of the pulmonary artery as it leaves the heart), or patent ductus arteriosis (PDA) which is when a small blood vessel that is meant to close off before birth remains open.

There are many other heart defects that can cause heart murmurs, including heart valve problems (the two main heart valves are the mitral valve and the tricuspid valve, but there are other valves too).

Some pedigree cat breeds are more prone to heart disease of different kinds, including Maine Coons, and Ragdolls, but problems can also be seen in mixed breed cats (Domestic Shorthair or Longhair). Severe congenital heart problems may be obvious in very young kittens, but commonly they do not become apparent until the kitten has reached three or four months of age, when they become larger and more active, placing more stress on their cardiovascular system.

Acquired Cardiac Disease

Heart murmurs can also be caused by diseases that start in adult cats, such as heart muscle disease (e.g. hypertrophic cardiomyopathy or HCM).

Conditions Separate To The Heart

So-called “extra-cardiac” causes of heart murmurs include viral or bacterial infections, fever, pregnancy, obesity, emaciation, anemia, hyperthyroidism and hypoproteinemia. In these cases, the underlying disease may change the viscosity and flow of the blood, leading to the turbulence that causes the murmur.

Innocent Murmurs

In some cases, your vet may carry out a detailed investigation of your cat’s heart murmur only to find that there is absolutely nothing wrong with your cat. In these cases, the murmur is an incidental finding, of no significance, and it is known as “innocent” or “physiologic”. These murmurs tend to be quieter, with the cat showing no obvious signs of illness at all, but still, a work up may be needed to confirm that they are nothing to worry  about. Sometimes such murmurs are only temporary, e.g. in young growing cats, but they can happen at any age.

How Does a Veterinarian Discover the Cause a Heart Murmur?

1. Stethoscope

A heart murmur is nearly always diagnosed by a veterinarian listening to your cat’s heart with a stethoscope, often during a routine health check. Occasionally , if the murmur is very loud, a diagnosis can be made simply by feeling a buzz when a hand is placed on the cat’s chest (this is known as a “pre-cordial thrill”. As well as making the diagnosis, your vet will also note details about the murmur, as well as many other aspects of your cat’s heart, including heart rate and regularity.

Once a heart murmur has been identified, your veterinarian will normally recommend further diagnostic testing to find out the underlying cause.

2. Physical Examination

Any investigation of any problem in a cat starts with a careful, thorough physical examination of your pet.

3. Ultrasound Examination

Detailed analysis of a heart murmur is usually accomplished by carrying out an echocardiogram, or an ultrasound examination of the heart. Ultrasound of the heart enables detailed evaluation of the heart muscle, the heart chambers, the valves of the heart, and other structures around the heart.

4. X-rays

Your vet may recommend chest x-rays, to visualise the size and shape of your cat’s heart, as well as other structures in your cat’s thorax (chest)

5. Advanced Imaging

Rarely, other types of imaging such as CT or MRI scans may be carried out, to obtain very detailed visualisation of the heart and associated structures.

6. Electrocardiogram

An electrocardiogram (ECG) is a recording of the electrical activity in your cat’s heart: this can be a useful way of gaining extra information about your cat’s cardiac function, as part of a gold standard approach to an investigation.

7. Blood Pressure Measurement

High blood pressure is common in older cats and can contribute to heart murmurs, so it can be important to monitor this.

8. Blood Tests

If an extra-cardiac cause of a heart murmur is suspected (such as anemia or hyperthyroidism), a blood sample may be taken for laboratory analysis.

9. Referral To A Specialist

Your local veterinarian may recommend referral to a veterinary cardiologist, who has a special interest in cardiology.

What Are the Symptoms of a Heart Murmur in Cats?

There are usually no external symptoms (clinical signs) of a heart murmur in itself. If the heart murmur is severe enough to cause heart disease (such as congestive heart failure) , then signs such as coughing, difficulty breathing, rapid breathing or even collapse may be seen.

If the cause of the murmur is extra-cardiac, then other signs of illness may be seen, depending on the cause (e.g. anemia or hyperthyroidism).

What Is the Life Expectancy of a Cat With a Heart Murmur?

The life expectancy depends on the cause of the murmur: cats with benign or innocent murmurs will have a normal life span, while cats with heart murmurs caused by life threatening structural defects of the heart may only live for months or a few years. In some cases, sudden death of affected cats can even occur. This is why it’s  so important to gain an accurate diagnosis of the cause.

Treatment Options for Heart Murmurs in Cats

A heart murmur in cats does not necessarily need treatment at all. The important fact to remember is that the cause of the murmur must be identified accurately.

Innocent murmurs need no treatment whatsoever, as they are harmless. Murmurs caused by structural heart defects may lead to the necessity for treatment of heart failure in due course, depending on the  severity of the problem.

Murmurs caused by extra cardiac conditions require that those conditions should be treated, rather than specific treatment for heart disease.

Conclusion

If your veterinarian tells you that your cat has a heart murmur, be sure to ask them to determine the precise cause of the murmur, so that you can take appropriate action to help your cat.