Heart Murmur in Cats – Causes, Symptoms & Treatment

Heart murmur in cats

A heart murmur is an abnormal sound of the heart caused by the vibration of turbulent blood flow. Heart murmurs may be a sign of a serious underlying condition such as hypertrophic cardiomyopathy and birth defects or functional, innocent or physiologic (no disease). The heart muscle or the heart valves may be affected.

What conditions can cause murmurs in cats?

  • Anemia – Decreased number of red blood cells. There are a number of causes of anemia in cats.
  • Bacterial endocarditis – Bacterial infection of the heart valve.
  • Congenital (present at birth) heart defects such as pulmonic stenosis.
  • Heart valve disorders.
  • Heartworm – A potentially fatal type of roundworm which lives in the heart, lungs and pulmonary arteries.
  • High blood pressure (hypertension) – Is a condition in which the blood is pumped at an abnormally high pressure through the arteries.
  • Hypertrophic cardiomyopathy – Thickening of the left ventricular wall, papillary muscles, and septum.
  • Hyperthyroidism – Benign tumour of the thyroid gland.

Heart murmurs which are present at birth are usually due to congenital defects or functional murmurs. Some young kittens will have a detectable heart murmur which vanishes by the time they are a few months old.

Heart murmurs are graded I to IV, by intensity (loudness), using a stethoscope.

  • Grade I – Barely audible
  • Grade II – Soft, but can be heard easily
  • Grade III – Moderately loud
  • Grade IV – Loud
  • Grade V – Can be heard with stethoscope off the chest
  • Grade VI – Can be heard without a stethoscope

What are the symptoms of heart murmurs in cats?

A heart murmur is a symptom in itself and not a disease. Symptoms will depend on the cause of the heart murmur. Many cats will display no symptoms at all. Common symptoms may include:

Diagnosing the cause of heart murmurs:

  • X-rays to evaluate the heart.
  • ECG  (electrocardiogram).
  • Blood tests to look for underlying disease, check for anemia.

Treating heart murmurs in cats:

Treatment depends on the cause of the murmur and clinical signs and may include:

  • Anemia: Treating the cat for internal and external parasites, blood transfusions for severe anemia, antibiotics to treat feline infectious anemia.
  • Bacterial endocarditis: Antibiotics to control the infection.
  • Surgery to correct birth defects, if possible.
  • Pulmonic stenosis: Balloon valvuloplasty is the insertion of a balloon into the pulmonic valve to break down the obstruction.
  • Heartworm: At the time of writing, there are no approved medications to treat heartworms. Each cat is treated on a case by case basis. If there are no other symptoms, the vet may choose to sit and wait, it takes approximately 2-3 years for the heartworm to die. Cats displaying symptoms of heartworm disease may be given prednisone to help reduce inflammation. Bronchodilators may be required if your cat is experiencing breathing difficulty. Cage rest may also be recommended.
  • High blood pressure: Finding and treating the cause, if possible. Medications to bring down the blood pressure such as calcium channel blockers, beta blockers, ACE inhibitors and diuretics may be prescribed.
  • Hypertrophic cardiomyopathy – There is no treatment other than supportive care for HCM. This may include diuretics, blood thinning drugs, beta blockers to help the muscle relax.

As you can see, most cases of heart murmur have an underlying cause, which needs to be addressed.

No treatment is required for a murmur alone.