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Lions Foundation of Canada Dog Guides and its founding program, Canine Vision Canada, was established in 1983. It’s the largest school of its kind in Canada with its training school in Oakville and breeding facility in Breslau.


Canine heart disease is dangerous: What You Need to know

Doctor examining dogs heart beat with stethoscope

Heart Disease in Dogs

Did you know that heart disease is just as dangerous in dogs as it is in people?


Is your dog showing signs of fatigue on walks?

Heart disease 

Heart disease can be defined as any abnormality of the heart. Unlike diseases of many other organ systems, heart disease generally does not go away but almost always becomes more serious and may lead to death.

Abnormalities of the heart

Heart abnormalities include:

  • Congenital abnormalities (defects that are present at birth)
  • Disorders of physical structure, function, or electrical activity

Classification of heart disease

Methods used for heart disease classification include:

  • Whether the disease was present at birth or not (congenital or acquired)
  • Causes (for example, infectious or degenerative)
  • Duration (for example, long- or short-term)
  • Clinical status (for example, left heart failure, right heart failure)
  • Physical structure malformation (for example, hole in the heart)
  • Electrical disturbance (for example, irregular heartbeat)

Congestive heart failure (CHF)

Congestive heart failure (CHF) is not a specific disease but a condition in which congestion or an abnormal accumulation of fluid, decreased blood flow to the body, and/or abnormally low blood pressure arise as the final consequence of severe heart disease. CHF manifests as a vicious cycle that begins when cardiac output decreases and the heart is no longer able to pump out the volume of blood it receives effectively.

As cardiac output reduces, compensatory mechanisms, such as the sympathetic nervous system (SNS) and renin-angiotensin-aldosterone system (RAAS) increases in activity to compensate. Water is retained, which leads to increased blood volume and excessive vasoconstriction, increasing vascular resistance and making it harder for the already failing heart to maintain cardiac output and tissue perfusion.

Heart disease and abnormalities of the cardiovascular system

The following abnormalities of the cardiovascular system can lead to heart disease:

  • Heart valves fail to close or open properly. Mitral valve disease (MVD) arises when damage to heart valve leaflets prevents them from closing properly, allowing blood to leak backward into the atrium
  • Dilated Cardiomyopathy (DCM) directly affects the heart muscle where the dog’s heart fails to pump effectively. Heart contractions are weak and therefore blood is not pumped through the body efficiently. Typically, the heart stretches and enlarges, which over time further decreases its ability to pump blood efficiently around the body
  • Heart beats too slowly, too rapidly, or irregularly
  • Blood vessels offer too great an interference to blood flow (vascular disease)
  • There may be openings between chambers of the left side and right side of the heart or abnormal blood flow between the body and the lungs
  • There is too little or too much blood compared with the ability of the blood vessels to store that blood
  • There are parasites of the cardiovascular system, such as heartworm disease

Common signs associated with heart disease

Signs of heart disease in dogs include:

Fainting, exercise intolerance, weakness

Because of inadequate blood flow, vital organs such as the brain can become deprived of oxygen. Fainting that may resemble a seizure could occur when blood flow to the brain is decreased. A fainting episode in dogs with heart disease can be triggered by increased activity or exercise and sometimes coughing. Dogs with heart disease will show exhaustion more quickly on walks and during exercise. They may sleep or rest more than usual.

Shortness of breath or elevated breathing

Difficulty breathing (dyspnea) can be a sign of heart disease. A dog may breathe more rapidly, or with more force. Some dogs will sit or stand with their legs wide apart and with their neck stretched out. Dogs with severe heart disease have more trouble breathing when lying down, and will often sit or stand for long periods of time.

Fluid accumulation in lungs and abdomen

Blood damming up in organs causes fluid to leak from blood vessels into tissues. This may result in an abnormal accumulation of fluid in the lungs or abdomen. Coughing that doesn’t resolve in a few days may indicate that fluid is accumulating in the lungs because the heart isn’t pumping efficiently. Blood is then ‘backed-up’ in the lungs, which can result in fluid leaking out of blood vessels and accumulating in lung tissue, resulting in cough. Fluid accumulating in the abdomen, giving the appearance of a ‘potbelly’, may indicate heart disease.

Blue tinged mucous membranes

When there is a lack of oxygen in the blood, the mucous membranes develop a blue tinge, and often there is an increased concentration of red blood cells.

Behaviour changes

Many behaviour changes can be seen in dogs with heart disease, including poor appetite, rapid weight loss, restlessness when sleeping, isolation and a reluctance to play or engage in previously pleasurable activities.

Diagnosing heart disease in dogs

Ask your veterinarian to examine your dog, if you notice any signs of heart disease. Veterinarians can often detect heart disease in dogs during routine office visits that include feeling your dog’s body, listening to their heartbeat with a stethoscope, and checking their gums. If your veterinarian suspects heart disease, one or several of the following procedures may be recommended:

  • X-rays
  • Cardiac evaluation
  • Electrocardiogram
  • Echocardiogram
  • Cardiac catheterization
  • Blood and urine tests

Treatment of heart disease in dogs

Your veterinarian will select a treatment designed for the type of disease. While specific defects can be repaired or corrected with surgery, other conditions can be managed with medical therapy using one or a combination of drugs. 

The goals of treatment are generally to:

  • Minimize damage to the heart muscle
  • Control the accumulation of fluids in the lungs
  • Improve circulation
  • Regulate the heart rate and rhythm
  • Ensure that there is enough oxygen in the blood
  • Minimize the risk of blood clot formation

If heartworm disease is diagnosed, your veterinarian will prescribe medical therapy to kill the mature heartworms and larvae.

Heart disease therapy is designed to resolve the signs, to bring breathing and heart rates to normal, and to provide your dog with a good quality of life.

For more information about heart conditions in dogs, visit our conditions and diseases section.

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Enlarged Heart (Dilated Cardiomyopathy) In Cats Read Now

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