Heart Muscle Diseases

Diseases of the heart muscle are less common than disorders of the valves. Dilated cardiomyopathy is, however, the second most common from of canine heart disease. Hypertrophic cardiomyopathy, although a common condition in cats and people, is rare in dogs; so, too, is myocarditis. The risk of heart diseases is inherited, particularly in certain breeds. It can be reduced by breeding from dogs whose lines are free of disease.

Dilated Cardiomiopathy

Dilated cardiomiopathy (DCM) affects relatively young dogs, usually under 7 years old, and sometimes as young as 2 years of age. In Cocker spaniels it may be associated with hypothyroidism. DCM may also be associated with immune system in the Doberman Pinscher. The breeds most commonly affected include the Boxer, Doberman Pinscher, Irish Wolfhound, Afghan Hound, Great Dane, Old English Sheepdog, and St. Bernard. The condition now is also being diagnosed in Dalmatians. DCM affects more males than females. Affected dogs are lethargic, tire easily from routine exercise, and often go off their food and lose weight. They may have a cough, especially at night.

Congestive heart failure (CHF) develops which leads to fluid accumulates in the lungs and in the belly. Both Boxers and Dobermans may die suddenly without showing any previous signs of illness. An ECG will show changes in the heart's rhythmic contraction, whilea chest X-ray will reveal that the heart has become enlarged. The dog is given treatment for congestive heart failure. Diuretic drugs such as spironolactone or furosemide diminish the buildup of fluid in the lungs and abdomen, while ACE inhibitors and a new drug, pimobendan (Vetmedin), improve the heart function and circulation. There is nutritional logic in supplementing the diet with taurine and L-carnitine, although the benefit of these nutrients is still being studied. The long-term outlook for an affected dog is rather poor, although the use of pimobendan has increased survival time threefold in Doberman Pinchers.

Vitamin D plays a pivotal role in cardiac function, and there is increasing evidence that vitamin D deficiency is associated with the development of congestive heart failure. Recent findings suggest that low concentrations of 25(OH)D, a measure of vitamin D status, may be a risk factor for CHF in dogs. Low serum 25(OH)D concentration was associated with poor outcome in dogs with CHF. Strategies to improve vitamin D status in some dogs with CHF may prove beneficial without causing toxicity.1

Hypertrophic Cardiomiopathy

Hypertrophic cardiomiopathy is characterized by the thickening of the heart. It usually affects the ventricles. As the muscle thickens, it reduces the space inside the heart for blood. The most common sign is reduced exercise tolerance. Hypertrophic cardiomyopathy is diagnosed by echocardiography. Treatment with the calcium channel blocker drug diltiazem appears to prolong life expectancy. Strenuous exercise should be avoided.

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Myocarditis is an inflammation of the heart muscle that has many possible causes. It is rarely diagnosed in dogs. It can be caused by infectious agents such as bacteria, viruses and parasites. Causes of myocarditis in dogs include viruses (e.g. parvovirus, West Nile Virus), protozoal agents (i.e. Trypanosoma causing Chagas disease, Toxoplasma, Hepatozoon, Babesia), bacteria (i.e. Staphylococcus, Streptococcus, Citrobacter, Bartonella, Borrelia), fungal agents (i.e. Coccidioides, Cryptococcus, Aspergillus), helminths (Toxocara) and non-infectious factors such as autoimmune reactions, toxins, trauma, heat stroke and hemodynamic shock. Clinical signs of myocarditis include lethargy, fainting and heart rhythm disturbances. After identifying the heart disease, and depending on the diagnosis, the dogs undergo appropriate pharmacological treatment or an electrical cardioversion procedure. The treatment for this condition is similar to that for congestive heart failure.

Infections from Ticks and Sudden Death

Recent evidence indicates that Bartonella. vinsonii is an important canine pathogen, and it has been shown as a cause of endocarditis granulomatous lymphadenitis, and granulomatous rhinitis. A survey of sick dogs from North Carolina and Virginia identified tick exposure as a risk factor for the detection of Bartonella. vinsonii antibodies. Infection with these organisms may contribute to fainting, collapse, arrhythmias, or sudden death.


  1. Relation of vitamin D status to congestive heart failure and cardiovascular events in dogs. J Vet Intern Med. 2014 Jan-Feb;28(1):109-15. doi: 10.1111/jvim.12239. Epub 2013 Nov 7.
  2. Myocarditis in dogs: etiology, clinical and histopathological features (11 cases: 2007–2013). Ir Vet J. 2014; 67(1): 28.
  3. Bartonella vinsonii subsp. berkhoffii and Related Members of the Alpha Subdivision of the Proteobacteria in Dogs with Cardiac Arrhythmias, Endocarditis, or Myocarditis. J Clin Microbiol. 1999 Nov; 37(11): 3618–3626. PMCID: PMC85709

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