Congestive Cardiomyopathy (Left-sided) in Dogs

The heart has four chambers: two chambers at the top, the right and left atria; and two chambers on the bottom, the right and left ventricles. The right side of the heart collects blood from the body and pumps it into the lungs, where the blood is oxygenated. The oxygen rich blood is then collected by the left side of the heart, and from there it is pumped out into the body's various organs.

Congestive left-sided heart failure refers to a condition in which the left side of the heart is not able to push blood through the body efficiently enough to meet the metabolic needs of the body, and frequently results in blood pooling in the lungs. This is the most common type of congestive heart failure in dogs. Low blood output from the heart causes tiredness, exercise intolerance and fainting.

Symptoms and Types

• Weakness
• Exercise intolerance
• Coughing and trouble breathing
• Dog stands in unusual positions to relieve pain
• Increased heart rate
• Crackles heard when listening to the lungs
• Pale/gray/bluish mucous membranes
• Gums stay pale longer than a few seconds when pushed upon with a finger
• Possible heart murmur
• Weak pulses on the insides of the dog's thighs

Causes

Muscle failure of the left ventricle (the left lower chamber of the heart):

• Dilated cardiomyopathy in older, large dogs (enlarged heart, cause unknown)
• Parasitic infection (e.g., heartworm infection, but this is rare)
• Drug toxicity
• Inactive thyroid (rare)
• Overactive thyroid (rarely causes pump failure; more commonly causes high blood output failure)

Pressure overload of the left heart:

• High blood pressure throughout the body
• Narrowing of the aortic artery (leads directly out of the heart)
• Left ventricle tumors (rare)

Volume overload of the left heart (the mitral valve on the left side of the heart, separating the left atrium from the left ventricle):

• Mitral valve bacterial infection
• Mitral valve abnormal development
• An abnormal hole in the wall dividing the ventricles (two bottom chambers of the heart)
• Aortic valve (valve separating the heart from the aortic artery which leaves the heart with oxygen-rich blood) failure due to bacterial infection

Difficulties filling the left heart with blood:

• Fluid filling the sac around the heart so that it has trouble beating
• Restrictive inflammation of the sac around the heart
• Restrictive heart disease
• Heart disease causing the heart to enlarge
• Left atrial masses (e.g., tumors and blood clots)
• Pulmonary blood clot
• Mitral valve narrowing (rare)

Heart beat rhythm disturbances:

• Slow heart rate
• Increased heart rate

Diagnosis

Your veterinarian will perform a thorough physical exam on your pet, taking into account the background history, onset of symptoms and possible incidents that might have led to this condition. A blood chemical profile, complete blood count, urinalysis and an electrolyte panel will be ordered to check the underlying cause of the heart disease and its severity. Your veterinarian will also draw blood from your dog to check thyroid function.

Imaging studies can be used to gain a further understanding of your dog's heart condition. X-ray and ultrasound imaging may be used, as well as electrocardiogram (ECG, or EKG) recordings for examining the electrical currents in the heart muscles. These recordings may reveal any abnormalities in cardiac electrical conduction (which underlies the heart’s ability to contract/beat).