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Feline Heart Murmurs (Abnormal Sound From Heart)

Heart Murmurs Guide:

Definition of Heart Murmurs in Cats

A heart murmur is an abnormal heart sound caused by the vibration of turbulent blood flow. Normally, blood flow is laminar and very quiet. Having a heart murmur is not itself an illness or disease. It is a characterization given to an abnormal sound heard upon auscultation over the region of the heart.

How Heart Murmurs Affect Cats

Cats of any age, breed or gender can be born with or later develop heart murmurs. Many affected cats show no outward signs of having heart murmurs. In fact, most murmurs are detected incidentally during routine veterinary check-ups. When heart murmurs do accompany clinical signs, generally there is something more serious going on with the animal’s heart and the murmur is a consequence of – not a cause of - that underlying condition. The signs are nonspecific and depend upon the cause of the heart disease. Some cats will become intolerant to activity or just generally “slow down.” They may pant while resting (open-mouth breathing is not normal in healthy cats) and have difficulty breathing. Their mucous membranes may become pale. The cat may cough and appear “pot-bellied” from fluid retention. Heart disease can cause a myriad of other symptoms in cats as well. In some cases, heart problems (possibly suggested by heart murmurs) can be associated with fainting spells or other periods of sudden collapse. This can happen when oxygen is not distributed properly to body tissues through normal blood circulation. If your cat’s gums become pale or even approach blue in color, be suspicious of inadequate oxygen supply and get your pet to the vet. This is cause for immediate concern.

Kittens frequently have “benign” heart murmurs (also termed innocent, functional or physiologic murmurs) which should disappear by 4 to 6 months of age. These are produced because the strong young heart is beating in close proximity to the kitten’s chest wall, and therefore the turbulence produced from blood flowing through the heart and large adjacent vessels can be especially prominent. These murmurs frequently are identified at the first kitty check up, and may vary in intensity depending on the animal's health and physical state. Follow-up veterinary examinations will track the murmur as the kitten matures.

Causes of Feline Heart Murmurs

Heart murmurs can be congenital (existing at birth) or acquired and can be caused by many different structural heart defects as well as by a number of infectious and other processes. Any of the heart valves (mitral, tricuspid, pulmonic, aortic) can be affected by endocardiosis, endocarditis, valvular stenosis or dysplasia, with characteristic heart sounds accompanying each type of disorder.

  • Endocardiosis is a common cause of cardiac disease and is characterized by chronic fibrosis and thickening of the free valve edges, causing anything from minor leakage to severe malfunction.
  • Endocarditis is an inflammatory change of the tissues lining the heart chambers and valves.
  • Stenosis is a narrowing or constriction of a body passageway that causes increased turbulence at the affected area. Pulmonic stenosis is a narrowing of the outflow area of the pulmonary artery at the exit from the right ventricle of the heart. The murmur reflects the abnormal turbulence that results where the outgoing blood meets resistance. Aortoic stenosis is a similar narrowing but occurs in the aorta outflow area, and the murmur develops for the same reason.

  • Dysplasia simply means an abnormality of development, such as some alteration in size, shape, organization or structure. Mitral valve dysplasia is one of the more common cat conditions. This defect results in a leaky mitral valve, and the murmur results from the turbulence of blood reflux.

Other causes of feline murmurs include, but are not limited to:

  • Atrial and ventricular septal defects - basically, a hole or tear of the interior wall separating the heart chambers. If the hole is very large, murmurs may actually be absent because of decreased turbulence.
  • Patent ductus arteriosus - a failure to close of an important duct in the fetal heart that will produce shunting of blood in the heart when it remains open after birth. If shunting occurs from the right to the left, murmurs are usually absent. However, in the usual left-to-right side PDA shunt, murmurs can be heard.
  • Cardiomyopathy - primary disease of the heart muscle, with several distinct forms in cats.
  • Feline heartworm infection
  • Tetralogy of Fallot - a complex congenital heart defect that combines four distinct structural anomalies of the heart and emerging arteries.
  • Hyperthyroidism
  • Anemia

Characteristic murmurs usually accompany each of these conditions and can be detected by skilled veterinarians through auscultation with their stethoscope.

Preventing Heart Murmurs in Cats

Murmurs are a clinical finding that cannot be “prevented” or even “treated” in the normal sense of those terms. The underlying cause of the murmur must be found. Many heart murmurs will never require medical or surgical management, even if they are very pronounced. Minor murmurs can often be managed with exercise and/or dietary change. Surgical procedures may be available for cats with more serious heart conditions causing their murmurs, although presently surgery is more commonly done in dogs.

Special Notes

If your veterinarian detects a heart murmur in your cat, she will likely recommend advanced diagnostics through use of thoracic radiographs, electrocardiography and/or echocardiography. You may be referred to a specialized veterinary cardiology to perform all or some of this testing. The prognosis for cats with heart murmurs depends almost entirely on the nature and severity of the underlying cause.

Remember, a heart murmur does not necessarily mean that the heart is in failure or otherwise diseased. Heart murmurs generally cannot be “cured,” because they are not a disease or illness per se, but their effects may be manageable with medication, exercise and dietary change.

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