Blood flows from the veins of the body into the right atrium. It is stored there briefly as it is pumped on into the right ventricle. The right ventricle pumps blood into the lungs, where it receives oxygen. It then flows from the lungs into the left atrium where it is held briefly before going on to the left ventricle. The left ventricle contains the largest muscle of the heart so it can pump blood out through the arteries to all parts of the body.

When Your Pet's Heart Fails:

There are two types of cardiac failure or myopathy that occur in dogs. In one form called hypertrophic cardiomyopathy the walls of the chambers of the heart thicken, leading to a decrease in pumping efficiency. This form of cardiac failure is quite rare in dogs. In the second form of cardiomyopathy the chambers of the heart increase in size and the muscles that form the walls of the heart stretch thinner. This is called dilated cardiomyopathy. This is the type that leads to congestive heart failure (CHF) in our pets. Canine Dilative Cardiomyopathy is one of the causes of CHF.

It is rather common for a dog’s failing heart to enlarge and no longer pump sufficient blood throughout the body. The most common cause of this in our pets as they age is damage to the valves that control the flow of blood within the heart. Pets are usually over five years of age when the condition is first noticed.

As the failing heart enlarges, the left side looses its ability to contract forcefully to pump blood through the body’s blood vessels. When this occurs, blood begins to pools in the right side of the heart, which supplies blood to the lungs for oxygenation and received spent blood from the thorax and abdomen. Sometimes the damage is more apparent on the right side of the heart first, sometimes on the left. But, eventually, both sides are affected because one relies on the other. The dog’s heart works hard to compensate for these changes but eventually your pet can no longer perform the activities it once did. This stage of the disease is called congestive heart failure.

In congestive heart failure, the heart is no longer able to provide blood with adequate oxygen to supply the body. Without adequate oxygen, the body's cells become desperate and trigger a series of responses. Various hormones are released by several organs in an attempt to correct the problem. These hormones conserve and retain fluids in an effort to increase blood volume and the output of blood. For several months, these compensatory responses help the situation. However, increased fluid retention eventually becomes harmful. More and more fluid leaks out of the capillaries, causing increased gagging and coughing, and reduced stamina. Fluid in the lungs is called pulmonary edema, fluid below the skin is called peripheral or limb edema, and fluid in the abdomen is called ascites. Peripheral or limb edema is much less common in dogs than in people with congestive heart failure.

What Are The Signs of Heart Failure?

Dogs in the later stages of congestive heart failure become much less active and tire easily. Their appetite usually falls of and they show signs of difficult respiration, panting and coughing while at rest. Their tummy enlarges and takes on a pear-shape as fluid accumulates in the liver and abdomen. Electrocardiograms taken of these dogs are always abnormal. When I examine these dogs, the color of the membranes of the mouth are grayish rather than healthy pink and blood vessels on the surface are abnormally congested with blood. These dogs often have a condition called a jugular pulse in which the beating of the heart can be seen in the large jugular veins of the neck. The sounds of heartbeat that I hear through my stethoscope are always abnormal to some degree.

By the time dogs become symptomatic with cardiomyopathy and congestive heart failure, they rarely live beyond a year. Many will die in six months. The disease is known to run in families so families with this problem should not be bred.

Dilated cardiomyopathy or congestive heart failure develops over many months or even years. Its effects on blood flow also develops slowly. As heart function declines, the body is able to compensate for several weeks or months. However, at some point, the body's ability to compensate is no longer effective. At this point, dogs go into severe heart failure in what appears to be a matter of hours. Rapid, heavy breathing, blue tongue, excessive drooling, or collapse may be the first signs that anything is wrong.

Why Did My Pet Get This Problem?

Nothing you did caused this problem. The disease runs in blood lines so it was probably preordained that your pet was susceptible to the disease.

How Is Cardiomyopathy Diagnosed In My Pet?

Heart failure is often suspected simply from the results of a veterinarian's physical examination of your pet. A stethoscope placed on the left side of the pets chest just behind the elbow allows the person listening to hear abnormal heart rhythms as well as abnormal sounds of blood whooshing through overly distended heart valves. Heart sounds in this condition tend to be muffled and the raspy noise of air passing through fluid-filled lungs is often audible.

To confirm suspicions, the veterinarian will obtain chest x-rays or a cardiac ultrasound image. Hearts in cardiac failure have a very distinctive globular shape. The normal, chiseled cardiac silhouette is replaced by a much larger, rounded heart shadow. Early in the disease the left side of the heart may be more enlarged than the right but with time both the left and right side of the heart enlarge. In boxers, rhythm irregularities may be present before x-rays show abnormal findings. The lungs of dogs in heart failure are abnormally dense due to fluid buildup within them.

Many veterinarians rely on electrocardiograms (EKG) to detect early heart abnormalities before x-ray diagnosis is possible. A fast, out-of-control fibrillation of the muscle of the atrium is present in seventy to eighty percent of giant dogs with cardiomyopathy. The portion of the paper tracing called the QRS complex lengthens and increases in height (amplitude) signifying left ventricular enlargement. Heart rate is faster than normal in the tracing and premature contractions of the ventricles give the tracing an abnormal rhythm.

Visualization of the heart in real time with an ultrasound also gives a good indication of the efficiency of the heart in pumping blood. It gives me the most accurate measure of the size of each heart chamber as well as some indication of the degree of heart enlargement as it is occurring in real time.

Blood serum chemistry and urine chemistry tests do not detect heart problems but they do let veterinarians know if problems in the liver or kidneys might affect the action of heart medications we will use.

Many cases of cardiomyopathy are accompanied by heart rhythm abnormalities. These are caused by disturbances in the electrical impulses that control heart rate and rhythm and they can be life threatening. It is a good idea to learn to check your dog’s pulse at its wrist to detect this abnormality at home. You may even choose to buy a nurse’s stethoscope for more accuracy.