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Heart Trouble


Filed in Cats, Dogs, Health

The heart is a truly amazing organ. The hearts of dogs and cats (and people) are made up of four chambers. Oxygenated blood enters the left atrium from the lungs via the pulmonary veins. It passes through the mitral valve into the left ventricle, out the aortic valve into the aorta, and out into the body. Blood returns to the right atrium of the heart via the vena cava. It passes through the tricuspid valve into the right ventricle. From the right ventricle, it is expelled through the pulmonic valve, into the pulmonary artery and on to the lungs where it is oxygenated. The anatomy is important to help us understand what occurs when there is a problem at a certain location within the heart.

Congenital heart defects are the most common cause of heart failure in animals less than one year of age. Sometimes a heart murmur in a young animal is not a significant finding. This is called an innocent murmur. Murmurs are graded from I to VI, depending on their characteristics and intensity of sound. A very quiet murmur (Grade I), in a young animal, may be simply an innocent murmur that will be gone at the next check-up.


Subaortic stenosis (SAS)

The most common congenital heart defect diagnosed in puppies is subaortic stenosis. This refers to a narrowing of the outflow path of the left ventricle, usually just below the aortic valve. These puppies usually don't have any symptoms initially and the problem is most often detected by the veterinarian at the physical examination. A murmur can be heard because of the turbulence of the blood flow as it is trying to exit the left ventricle. If the narrowing is severe, it can quickly lead to heart failure. Examination of the heart by ultrasound with Doppler will confirm the diagnosis of SAS

Breeds commonly affected: Newfoundland, Golden Retriever, Rottweilers, Boxer, German Shepherd, Samoyed

Treatment is generally not curative. Dilation of the narrowing is possible, but does not result in long term repair of the lesion. Medications can be used to help lessen the load on the heart. Sudden death often occurs in these patients, secondary to arrhythmias.

Pulmonic stenosis (PS)

This problem occurs on the opposite side of the heart from SAS. The outflow from the right ventricle is restricted either because of a narrowing of the outflow path (like in SAS) or because of abnormalities of the leaflets of the tricuspid valve. These valvular abnormalities are more common than narrowing of the pulmonary artery. Mild cases of PS will also result in minimal clinical symptoms. More severe cases will show exercise intolerance and progressive heart failure. Ultrasound and Doppler will help confirm this diagnosis as well.

Breeds sommonly affected: Beagle, English Bulldog, Mastiff, Fox Terrier, Samoyed, miniature Schnauzer, Cocker Spaniel, West Highland White Terrier, Chihuahua.

Treatments: Balloon valvuloplasty to open the abnormal valve is relatively successful in these cases. If the valve itself is small and malformed, treatment is not as successful.

Patent ductus arteriosus (PDA)

The ductus arteriosus is the connection between the right side of the heart and the placenta. This blood vessel allows blood to leave the fetus and go to the placenta to be oxygenated, bypassing the lungs (which don't work in the fetus). At birth, hormonal changes and environmental changes (such as the expansion of the lungs with air), cause the closure of this vessel. In cases of patent ductus arteriosus, the vessel remains as an open communication. This allows blood to bypass the lungs, decreasing oxygenation in the body and leading to congestive heart failure as the heart works harder and harder to get oxygen into the body. Examination (characterization of the murmur), radiographs, EKG, and ultrasound can help with the diagnosis.

Breeds commonly affected: Poodles, German Shepherd, Collies, Pomeranians, Shetland Sheepdog, Maltese, English Springer Spaniel, Keeshond, Yorkshire Terrier

Treatments: This particular defect can be surgically corrected or even corrected with catheterization and implantation of a coil in the ductus. After repair, prognosis for a normal life is good.


Congenital heart defects in kittens are not nearly as common as they are in puppies. They can suffer from the same defects, but ventricular septal defect is one of the most common.

Ventricular septal defect (VSD)

The most common congenital defect in kittens, a VSD is a communication between the right and left ventricle. These can be of variable size and may or may not cause significant problems. Some cases (especially in dogs) are thought to resolve on their own. The potential problem here is the shunting of blood across the defect, overloading one side of the heart, leading to heart failure.

Breeds: No breed predilection is known.

There is not a good treatment option. Supportive care and medical management of the heart failure will help keep the kitten comfortable.

Adult Dogs

Adult dogs are most likely to suffer from one of two types of heart disease. Small dogs typically develop mitral valve insufficiency as they age and large dogs develop dilated cardiomyopathy. In areas where heartworms are a problem, this would be another common type of heart disease affecting any adult dog, but this requires another article.

Mitral Valve Insufficiency (MVI)

This is by far the most common heart problem generally seen in private practice. As dogs age, the mitral valve can become weakened or damaged. It doesn't close tightly and blood leaks back into the left atrium from the left ventricle. Because of this backwards flow, a murmur can be heard with a stethoscope. Over time, the left atrium enlarges, and the valve becomes less able to form a tight seal between the two chambers of the heart. The heart works harder to pump blood out to the body, but there is less blood than normal in the left ventricle. Heart failure is the end result. The problem can be diagnosed by physical examination, radiography, EKG, and ultrasound.

Breeds: small breed dogs

Treatment is aimed at improving the function of the heart, preventing further damage to the valves, and managing heart failure. There are many good medications that can help these dogs live good quality lives for some years after a diagnosis of MVI.

Dilated Cardiomyopathy (DCM)

Dilated cardiomyopathy is an inherited disease affecting large breed dogs. DCM is a disease that affects the heart muscle itself. Initially, the left ventricular muscle weakens and expands. The pumping ability of the muscle is lessened. Pressure increases in the atria of the heart and heart failure (manifested by pulmonary edema) results. Arrhythmias are a part of this disease, typically atrial fibrillation is seen.

Breeds commonly affected: Doberman Pinscher, Great Dane, Newfoundland, and Irish Wolfhound.

Treatment involves managing the heart failure. No cure is known. In a limited number of cases, a taurine deficiency has been diagnosed in the early stages of the disease. Supplementation with taurine can halt progression of the disease in these cases.

Adult Cats

Again, cats don't have the same list that dogs do. Adult cats are susceptible to heartworms, like adult dogs. In addition to this, they usually suffer only from hypertrophic cardiomyopathy.

Hypertrophic cardiomyopathy

This disease is an inherited disease that manifests in adulthood. It is a disease of the heart muscle, like dilated cardiomyopathy in dogs. Hyperthyroidism and systemic hypertension can cause thickening of the left ventricular wall. This is not the same as hypertrophic cardiomyopathy, which is a primary disease of the heart. These diseases should be ruled out before pursuing treatment of primary hypertrophic cardiomyopathy. A heart murmur or abnormal sounding heart rhythm can be heard with a stethoscope. An ultrasound is used to confirm the diagnosis. Thickening of the walls of the heart leads to a decreasing size of the chambers of the heart (where the blood goes). Pressure increases in the heart and fluid can build up in the lungs as the disease progresses to congestive heart failure. Another symptom that develops in cats is a paralysis of the back legs. This occurs when a blood clot forms and flows through the body, ending up at the arteries that supply the back legs. This painful condition can be treated, but is usually a bad sign that the disease has progressed.

Breeds Affected: Maine Coon, Ragdoll, Rex, American Shorthair, British Shorthair

Treatment with medications may alleviate the symptoms of heart failure, but no cure is available.

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