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ASK THE VET: Dogs with heart murmur often have chronic valve disease

by Lee Pickett, VMD, Creators | May 8, 2023 at 2:09 a.m.

Q: My 7-year-old, 20-pound, mixed breed dog has a heart murmur. Her veterinarian thinks it's due to chronic valve disease. What is this?

A: Each time a normal dog's heart beats, it produces two sounds: lub-dub. A murmur is an extra sound, for example, a "swish," as in lub-swish-dub.

In dogs under 45 pounds, the most common cause of heart murmurs is chronic valve disease. Ten percent of dogs have heart problems, 75% of which are chronic valve disease.

This disorder is most often inherited. Small-breed dogs are at increased risk, especially if they are male. The disease usually becomes apparent when the dog is middle-aged or older, but it can develop earlier in Cavalier King Charles Spaniels.

Chronic valve disease is caused by thickening of one or more of the four valves that regulate blood flow through the heart. Usually affected is the mitral valve, which separates the upper and lower chambers of the left side of the heart.

The valve and the cords that hold it in place thicken so much that the valve can't close completely when the heart contracts. This allows blood to flow backward into the previous chamber, creating the murmur.

Chronic valve disease usually progresses slowly in small-breed dogs but faster in large-breed dogs. Generally, the murmur is heard before the dog develops obvious problems.

Clinical signs progress from a cough and decreased stamina to breathing difficulties and diminished appetite.

Diagnosis is made by echocardiography, an ultrasound of the heart that shows not just whether a valve is thickened and leaky but also how effectively the dog's heart can pump blood.

Chest radiographs (X-rays) reveal whether the disease has progressed to heart enlargement, or even congestive heart failure, fluid backup in the lungs.

Medication and dietary modification help the dog feel better and prolong life. It's also important for overweight dogs to lose weight. Surgical repair of the affected valve can be considered in advanced stages.

Q: Why do Siamese cats have dark ears, feet and tails?

A: Many cat breeds, including Siamese, Himalayan, Ragdoll and others, have a pale trunk and darker "points."

This striking color pattern is caused by a gene mutation that affects the activity of an enzyme needed to create melanin pigment. In cats with points, the enzyme produces melanin at low body temperatures but fails to function at normal body temperature.

Siamese kittens are born nearly white, because the mama cat's womb is uniformly warm. But as the cat ages, melanin is produced where the body is coolest — the ears, face, feet, lower legs and tail — which gives rise to the stunning coat pattern.

Lee Pickett, VMD, practices companion animal medicine in North Carolina. Contact her at

Print Headline: Dog’s heart murmur often is caused by chronic valve disease


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