Heart and Lung Diseases in Cats


PetMD Editorial

Published Jul. 16, 2008

Endomyocardial Diseases in Cats

Endomyocarditis, or inflammation of the inner heart muscle and lining, is an acute heart and lung (cardiopulmonary) disease that typically develops following a stressful event. It is characterized by interstitial pneumonia, and inflammation of the innermost portion of the heart. Pneumonia is usually severe and commonly results in death.

Endomyocarditis occurs predominantly in males, between the ages of 1 and 4 years. The development of biventricular endocardial fibroelastosis (occuring within both heart chambers) or left heart failure, meanwhile, occurs prior to 6 months of age. Endocardial fibroelastosis is an inherited (congenital) heart disease in which severe fibrous thickening of the muscular tissues within the heart leads to heart failure.  Moderator bands are normal muscular bands in the right lower chamber (ventricle) of the heart that can sometimes occur in the left lower chamber. Excessive moderator bands (EMBs) is a rare and unique pathologic disease. EMBs can be seen at any age.

Symptoms and Types


  • Shortness of breath following a stressful event in a young, healthy cat
  • Respiratory signs usually occur 5–21 days after the event
  • In 1 report, 73% of cases occurred between August and September

Endocardial Fibroelastosis and EMB

  • Heart gallop
  • Systolic murmur, reversal of blood flow through heart valves
  • Shortness of breath and increased lung sounds, or crackles
  • Weakness or paralysis with weak or absent pulse
  • Abnormal heart rhythm (arrhythmia) is possible


Generally, the causes for endocardial fibroelastosis or endomyocarditis are uknown. Risk factors for endomyocarditis include stressful incidents, such as anesthesia (commonly associated with neutering or declawing), vaccination, relocation, or bathing. Endocardial fibroelastosis, meanwhile, may be due to genetic factors; it is often seen in Burmese and Siamese cats.



  • No one standard therapy to date
  • Small percentage of cats have survived on long-term therapy
  • Supportive care with oxygen and ventilation

Endocardial Fibroelastosis and EMBs

  • Oxygen therapy via cage delivery is least stressful
  • Lung membrane tap if necessary

Living and Management

Expected Course and Prognosis:

  • Endomyocarditis — Poor, although some animals survive; endomyocarditis may progress to left ventricular endocardial fibrosis
  • Endocardial fibroelastosis and EMBs — medical treatment may prolong life, but recovery is unlikely.

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