Heart Murmur in Cats

Last Updated on July 9, 2021 by Julia Wilson

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 heart valves may be affected.


  • Anemia – Decreased number of red blood cells, with a number of causes. 
  • 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) – A condition in which the blood is pumped at 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.

The veterinarian will grade heart murmurs from one to four by the intensity with the use of a stethoscope.

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


A heart murmur is a symptom in itself and not a disease. Symptoms will depend on the cause of the heart murmur, and many cats will be asymptomatic.


A thorough physical examination, medical history and diagnostic workup will be needed to determine the underlying cause as well as evaluate the overall health of the cat.



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. Treatment is 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 who display symptoms of heartworm disease can receive prednisone to help reduce inflammation. Bronchodilators if the cat is experiencing breathing difficulty. Cage rest will also be necessary.
  • High blood pressure: Find and treat the cause, if possible. Medications to bring down the blood pressure such as calcium channel blockers, beta-blockers, ACE inhibitors and diuretics.
  • Hypertrophic cardiomyopathy – There is no treatment other than supportive care for HCM, which may include diuretics, blood-thinning drugs, beta-blockers to help the muscle relax.

Most cases of heart murmur have an underlying cause, which requires treatment.

No treatment is necessary for a murmur alone.