Heart murmur is a common finding in cats. Our veterinarians have answered the most common questions about it.
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What is a heart murmur?
A heart murmur is an additional heart sound your veterinarian can hear using a stethoscope.
What causes a heart murmur in cats?
A heart murmur results from blood turbulence in the heart chambers or large blood vessels coming to and from the heart.
There are multiple potential causes of heart murmurs in cats. Depending on the cause, veterinarians classify murmurs into several groups.
Functional (innocent and physiologic) murmurs
Functional murmurs are the term veterinarians use to describe heart murmurs that do not indicate any underlying heart disease.
No cause (i.e., source of a murmur) can be found in cats with so-called innocent murmurs, which frequently occur in kittens.
In contrast, in physiologic heart murmurs in cats, the cause of a murmur can be found, but it is not related to the heart disease. These murmurs can happen due to stress and excitement, pain, anemia, pregnancy, high blood pressure, and other reasons that increase the amount of blood pumped out of the heart with each heartbeat or make the blood too thin.
Some functional murmurs in cats can be transient. That means they come and go, and your veterinarian will hear them only intermittently.
Pathologic murmurs
These murmurs are caused by heart disease. They can be congenital and present from birth or appear later in life.
Some diseases never progress to the stage when the dog has clinical signs. Because of that, a pathologic murmur does not always mean the dog will have symptoms or die.
Can stress cause a heart murmur in cats?
Yes, sometimes cats can have a murmur at the exam due to stress. Such a murmur will most likely be quiet.
Undoubtedly, it still might be a good idea to rule out other more serious potential causes of a murmur.
Hyperthyroidism and a heart murmur in cats
Hyperthyroidism is a common disease in older cats. It happens when thyroid glands overproduce thyroid hormones.
The disease leads to increased metabolic rates.
Among other effects, it causes an increased blood flow through the heart and can result in high blood pressure and hyperthyroid hypertrophic cardiomyopathy. In turn, all of those can be a reason for a heart murmur.
In the case of hyperthyroidism in your cat, the veterinarian will likely recommend treatment for that disease.
Heart murmur in cats with kidney disease
Cats with kidney issues and chronic renal disease can have a heart murmur due to anemia, high blood pressure, or other causes.
What are the stages, levels, or grades of a heart murmur in cats?
Veterinarians often grade murmurs on a scale from 1 to 6 (I to VI) and denote them as 1/6, 2/6, 3/6, 4/6, 5/6, or 6/6, or the same in Roman numerals.
The first number shows how loud the murmur is on a scale of 1-6 out of 6, where 1 is the quietest, and 6 is the most pronounced and most audible.
- Grade 1 heart murmur is soft, quiet, and hard to hear. It is easier to notice in a quiet room and with a calm cat.
- Grade 2 heart murmur in cats is also quiet but the vet will easily hear it.
- Grade 3 murmur is of moderate intensity.
- Grade 4 heart murmur in cats is a loud murmur, sometimes radiating to other areas.
- Grade 5 murmur is also loud, but your veterinarian will also be able to feel a so-called precordial thrill – a vibration felt when you hold your hand against the chest wall and breastbone where the heart is.
- Grade 6 murmur is so loud that the veterinarian will hear it even when moving their stethoscope off the cat’s chest. The thrill (vibration you can feel) is also present.
What is a low-grade murmur?
Low-grade heart murmurs are quiet. Many veterinarians will deem any murmur of grade 1 or 2 or any soft and mild heart murmur in cats low-grade.
What are the symptoms of a heart murmur in cats?
There are no signs of a heart murmur or disease in kittens and cats with innocent murmurs.
In some cases of physiologic murmurs, symptoms of non-cardiac disease that caused a murmur might be present.
In cats with a heart condition and a murmur, symptoms of heart disease may be present. The most common ones are:
- Faster breathing and difficulty breathing
- Slowed growth in kittens, weight loss
- Change in mood, hiding
- Decreased appetite
Cats do not typically cough due to heart disease, which sets them apart from dogs, in whom cough is a very common symptom.
How to diagnose a heart murmur?
The veterinarian will listen to your cat’s heart to diagnose a heart murmur.
They might also recommend the next step, a cardiologist’s exam with a heart ultrasound (echocardiography) to determine what causes a murmur.
Is treatment for heart murmur in cats needed?
Veterinarians do not treat heart murmurs per se. Instead, the condition that caused a murmur might need treatment.
To ease your worries, studies show that more than half of cats with heart murmurs do not have structural heart disease and, as such, do not require treatment.
When therapy is needed, it will be based on the cause of the murmur. Some heart diseases require surgical treatment, while others can be treated medically.
Heart murmur in cats and anesthesia
Anesthesia can be done safely in many cats with a heart murmur.
Please tell your veterinarian that your cat has a murmur before scheduling any procedures that require anesthesia.
Veterinarians often recommend additional diagnostics before anesthesia to determine what causes the murmur and how serious it is. This will help to plan anesthesia accordingly.
When a severe condition causes a murmur, your veterinarian might recommend treatment beforehand.
Some cats with murmurs will benefit from scheduling procedures under anesthesia in specialist veterinary hospitals, where board-certified anesthesiologists perform all anesthesia compared to general practice veterinarians or technicians in general practice hospitals.
Heart murmur in cats and surgery
Veterinarians do perform surgical procedures on cats with heart murmurs.
If your cat has a murmur, let your veterinarian know beforehand. They will advise you on what can be done to lower the risk of complications.
A cardiologist’s exam might be recommended to clarify the cause of a murmur and establish a good plan for anesthesia and surgery.
Some cats might require treatment or postponing the surgery if it is not urgent.
Please look at the information on anesthesia in cats with heart murmurs above.
Life expectancy in cats with a heart murmur
The murmur itself and its grade cannot predict a cat’s lifespan. A prognosis will largely depend on the cause of a murmur.
Some cats with murmurs live a long and happy life. Others can succumb to heart disease in a short time or years later.
Ask your veterinarian about the typical lifespan of cats with similar pathology to know what to expect and if there is something you can do to prolong your pet’s life.
References
Ferasin L with colleagues. Prevalence and clinical significance of heart murmurs detected on cardiac auscultation in 856 cats. Last accessed on March 6th, 2024.
Ljungvall I. Heart murmurs in cats – what do they mean? Last accessed on March 6th, 2024.