I.Heart Anatomy

The heart in the dog is very much the same as a human heart; it just sits differently within the chest. The heart has four chambers which pump blood into and out of the lungs and then to the rest of the body. The left side of the heart consists of the left atrium and ventricle. The left atrium gets blood that has just picked up oxygen from the lungs. This blood goes into the left ventricle and then out through the aorta to the rest of the body to deliver oxygen to all of the tissues and organs. Blood returns to the heart from the body though the vena cava into the right atrium. From the right atrium, it goes into the right ventricle and then through the pulmonary artery and into the lungs to get rid of carbon dioxide and pick up oxygen.

The left side of the heart stays at a high pressure because it must pump blood a long distance to reach body tissues. The right side of the heart stays at a lower pressure because blood must only travel to the lungs, which are much closer to the heart.

There are four important valves in the heart which prevent blood from flowing in the wrong direction. The mitral valve is between the left atrium and ventricle. The tricuspid valve is between the right atrium and ventricle. The aortic valve is between the left atrium and the aorta and the pulmonic valve is between the right atrium and the pulmonary artery.

The Normal Dog Heart

The sounds that a veterinarian hears when listening to the heart are the sounds of the valves closing to prevent back-flow of blood. The mitral and tricuspid valves close at approximately the same time, and the pulmonic and aortic valves close at about the same time. This results in two sounds, “lub” and “dub”. The sound of a beating heart is just the repetition of “lub-dub, lub-dub, lub-dub…”

II.What is a Heart Murmur? What Causes a Heart Murmur in an Older Dog?

Normally, the blood flowing through the heart and the large blood vessels near it (aorta and pulmonary artery) moves smoothly and in only one direction. When blood does not move smoothly (is turbulent), it makes noise that is heard as a heart murmur. A heart murmur sounds like a swishing sound that happens between “lub” and “dub” or between “dub” and the next “lub.

In older dogs, the most common things that may cause turbulence in the blood include:

• Disease or dysfunction of one of the heart valves. This allows blood to move backwards when it should not be able to. It meets up with blood that is trying to move forwards creating turbulence and a heart murmur


• Diseases of the heart muscle. In dogs, the heart will enlarge and the muscle walls will become thinner, as the heart enlarges, the valves are pulled apart and no longer close the way they should. This leads to turbulence and a heart murmur.

Heart murmurs in older dogs are most commonly caused by:

• Mitral or Tricuspid Valve Insufficiency. Mitral valve insufficiency is much more common than tricuspid valve insufficiency. It usually happens in small breeds of dogs that are at least seven years old. There may be an inherited tendency for the mitral valve to degenerate with age. With mitral insufficiency, the mitral valve degenerates and becomes thickened. When this happens, it does not close correctly and allows blood to flow backwards from the left ventricle into the left atrium. This backflow of blood causes turbulence and creates the murmur. Eventually, the backflow of blood may cause the left side of the heart to malfunction leading to heart failure.


• Cardiomyopathy. In dogs this is usually dilated cardiomyopathy. This is mostly seen in large and giant breed dogs particularly Doberman Pinschers, Boxers, and Cocker Spaniels. In dilated cardiomyopathy, the heart becomes enlarged and the heart muscles thin and are unable to contract and pump blood effectively. This leads to congestive heart failure and to abnormal heart rhythms

III.What to Watch for at Home – Symptoms

Many heart murmurs caused by mitral insufficiency or cardiomyopathy may first be noted during a routine examination at the veterinarian’s office. At this time, the dog may have no symptoms. The symptoms of mitral insufficiency usually occur gradually and may not always be noticed. Some symptoms to watch for at home that may be caused by mitral insufficiency include:

• Coughing, sometimes heard more at night


• Difficulty breathing


• Rapid respiratory rate


• Lack of energy


• Inability to exercise normally


• Fainting or passing out when exercising

Many of these symptoms are related to congestive heart failure and only appear when mitral insufficiency is advanced.

With cardiomyopathy in dogs, the symptoms usually come on suddenly. They include:

• Difficulty breathing


• Fainting or passing out


• Coughing


• Inability to exercise normally


• Bloating or distension of the belly


• Lack of appetite


• Weight loss


• Lack of energy

Some dogs with cardiomyopathy may have no symptoms, but may have an abnormal heart rhythm that is detected during a veterinary examination. Unfortunately, some large dogs such as Dobermans and Boxers with cardiomyopathy may die suddenly without any symptoms.

IV.The Veterinary Visit – What is Causing My Dog’s Heart Murmur?

In many older dogs with mitral insufficiency or cardiomyopathy, a heart murmur or irregular heart beat may be noticed at the veterinarian’s office before any symptoms develop. Based on the age of the dog and the breed of the dog, the veterinarian may make an initial, tentative diagnosis of what disease is causing a heart murmur in an older dog. To confirm this diagnosis, chest x-rays will be taken. On the chest x-ray, the veterinarian is looking to see if the heart is enlarged or if there is any fluid in the lungs.

If a dog has an irregular or abnormal heart rhythm, the veterinarian will also do an ECG or electrocardiogram. These are most often used in large dogs with cardiomyopathy to see exactly what rhythm problem is present and how severe it is.

In most cases, these are the only two tests that will need to be used to diagnose which heart disease is present and how severe it is. In some cases, a cardiac ultrasound (echocardiogram) will be needed. This lets the veterinarian look at the inside of the heart, at the function of all of the valves, and at the thickness of the muscles while the heart is beating. A cardiac ultrasound can be used for diagnosis and also to see how well a dog is responding to therapy.

Before therapy is begun, the veterinarian may run complete blood work also. Some heart medications can affect the function of the kidneys and other organs and it is important to know what they are doing before starting treatment. Blood work will also help a veterinarian decide if there is an infection in the body that might be affecting the heart or heart valves. The video shown below talks about diagnosis and treatment of heart disease in dogs:

V.Treatment

Treatment will depend on which disease a dog has and how severely it is affected.

Mitral Insufficiency

Some dogs with mitral insufficiency and no symptoms may not need to be treated. These are dogs that have a normally sized heart on chest x-rays, a normal ECG, and no symptoms. In these cases, the veterinarian will want to take chest x-rays and do an ECG on a regular basis to see if the heart is getting larger or heart rhythm abnormalities are appearing. If the heart seems to be enlarging or if symptoms develop, then treatment is necessary. For all dogs that have symptoms of heart failure, treatment is necessary. It is usually a combination of one or more of the following depending on how severe the disease is:

• Low salt diets


• Diuretics such as furosemide. These medications will help pull excess fluid out of the lungs and make it easier for a dog to breathe.


• ACE Inhibitors. Examples of this type of drug are enalapril and benazepril. These drugs help decrease symptoms and also help decrease the work load on the heart making it easier for it to pump.


• Pimobendan. This drug helps decrease the work load on the disease heart and makes it easier for it to pump blood.

Many dogs with mitral insufficiency do well with therapy and live for many more years on medication. Some dogs with severe congestive heart failure may not do this well.

Cardiomyopathy

Treatment of cardiomyopathy is very similar to treatment of mitral insufficiency. All of the drugs mentioned above may be used to treat a dog with cardiomyopathy and heart failure. In addition, some other types of drug may be used:

• Antiarrhytmic drugs. An example of an antiarrhytmic drug is digoxin. These types of drugs are used to help normalize the rhythm of the heart and slow the heart down.


• Beta-blockers. An example of a beta blocker is atenolol. In dog’s whose heart rate is too fast or the heart rhythm is still abnormal even on digoxin, a beta –blocker may be added to further slow the heart rate and control the heart rhythm.


• Calcium channel blockers. An example of a calcium channel blocker is diltiazem. These are used for the same thing that beta-blockers are used for


• L-Carnitine. This is an amino acid supplement that may help some dogs with dilated cardiomyopathy.

Dilated cardiomyopathy can be challenging to treat. The prognosis for dogs with cardiomyopathy is guarded with an average lifespan after diagnosis of two to twenty-four months. Dobermans, in particular, do not do well for very long.