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.

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 a Puppy?

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.”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


• A hole between heart chambers that should not be there. For example, a hole between the left ventricle and the right ventricle allows blood to move from the left ventricle to the right ventricle. It meets up with blood trying to move out of the right ventricle and creates turbulence.


• A hole between two large blood vessels near the heart that should not be there. This allows blood to flow from one vessel to the other when it should not. This creates 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 puppies are most often due to heart defects that they are born with. The most commonly seen heart defects are:

• Patent ductus arteriosus. This is the most common heart defect in puppies. It is actually an open connection between the pulmonary artery and the aorta. This connection is normally present in all puppies before they are born. It carries blood from the aorta and back into the rest of the body’s circulation, bypassing the lungs. When a puppy is in the uterus, the mother dog supplies oxygen for the puppies and the puppy’s lungs are not needed. This connection usually closes within hours after birth and blood starts to flow through the puppy’s lungs to get oxygen. When the connection does not close, blood flows from the aorta through the connection into the pulmonary artery.


• Subaortic stenosis. This defect occurs when a tight band of tissue is present near the aortic valve. The band of tissue causes narrowing of the aortic valve area. This increases the pressure on the aortic valve which eventually leads to malfunction of the valve. When the aortic valve malfunctions, blood can flow back and forth between the aorta and left ventricle which causes turbulence.


• Pulmonary Stenosis. Pulmonary stenosis is narrowing of the pulmonic valve area. This is similar to aortic stenosis just with a different valve. Most dogs that have this also have malformation of the pulmonic valve itself.


• Ventricular Septal Defect. This defect is a hole in the wall between the left ventricle and the right ventricle. This hole allows blood to flow from the left ventricle into the right ventricle

III.What to Watch for at Home – Symptoms

Most puppies do not have symptoms associated with their heart defect. Usually, it is only picked up during an early routine veterinary visit. Some symptoms which may occur include:

• Coughing


• Difficulty breathing


• Lack of energy


• Inability to exercise like a normal puppy – seems to wear out too soon


• Fainting or passing out


• Fluid build-up in the belly, or a bloated appearing abdomen

Many of these symptoms are related to heart failure. They are usually only seen with severe defects or defects that go undiagnosed and progressively get worse until the heart begins to fail.

IV.The Veterinary Visit – What is causing My Puppy’s Heart Murmur?

Most puppies do not have symptoms associated with their heart defects so most owner’s are unaware that anything is wrong until they take the puppy in for vaccinations. During the visit, the veterinarian will hear a heart murmur. Some heart murmurs, such as that associated with a patent ductus arteriosus, have a very distinctive sound. This alone may cause the veterinarian to be suspicious of a certain type of heart defect. In many cases, however, they type of heart defect cannot be diagnosed by listening to the murmur. After hearing a suspicious murmur, the next step in diagnosis is chest x-rays. Some heart defects cause very specific changes to the heart that allow a diagnosis to be made just from x-rays. In many cases, however, a heart ultrasound will be needed. Not only will this provide a specific diagnosis, but it will allow measurement of the defect, which may help in determining the correct treatment or in predicting how a puppy will do for the rest of it’s life.

Not all heart murmurs in puppies are associated with heart defects. They are what is called “innocent murmurs.” These are very soft heart murmurs that usually go away by the time a dog is four months of age. The heart murmurs that occur with heart defects are usually very loud and distinctive.

V.Treatment

Treatment varies depending on the type and severity of the defect present.

• Patent Ductus Arteriosus. Treatment for a PDA is to surgically close off the connection between the aorta and the pulmonary artery. In some dogs this requires surgery to open the chest. Some dogs, however, can have a small coil implanted in the opening using a catheter that is inserted through a blood vessel in the leg. A blood clot forms around the coil closing off the connection. Patients usually do well after surgery especially if they have surgery before they are a year old and before they have symptoms of heart failure. If patients do not have surgery, the majority of them die within the first year or two of life. It is rare for them to live to the age of five.

A Patent Ductus Arteriosus

• Subaortic Stenosis. Treatment for subaortic stenosis depends on the severity of the defect. Dog’s that have a very mild defect may not be treated at all. Dogs with a moderate defect and some symptoms may be treated with medications to manage heart failure. In some cases, surgery can be used to try and dilate or open up the aortic valve area. This may only help temporarily and a ring of scar tissue may reform in the area where the dilation procedure was done. In some cases, open heart surgery may be done to surgically correct the defect.


• Pulmonary Stenosis. Dogs with a mild pulmonary stenosis and no symptoms of heart failure may not need treatment at all. Dogs that have a severe defect or symptoms of heart failure may be treated with surgery. As with subaortic stenosis, dilation of the narrowed area is used in some cases. In some cases, the defect may actually be surgically correctable.


• Ventricular Septal Defect. Small ventricular septal defects do not need to be repaired. Dogs with larger ventricular septal defects may undergo surgery to repair the defect. For dogs that develop symptoms, medication is given to manage heart failure.

How well a puppy with a heart defect does depends on how severe the defect is. Many puppies go on to lead long normal lives even if their defects cannot be corrected. For dogs that have severe defects and develop heart failure, the prognosis is guarded and depends on how well they respond to treatment for heart failure.

None of the information in this article is designed to diagnose or treat your dog. If you suspect a problem, see your veterinarian immediately for appropriate diagnosis and treatment.