For an older dog, a heart murmur may be an early sign of heart failure. But don’t take the discovery as a death sentence.

At Fido’s last vet visit, I learned that he has a heart murmur, probably a leaky mitral valve. Definitely a sign of aging and something to watch.

As I struggled to process how a dog who can still spin, sprint and double-back playing “Crazy Dog” could have a failing heart, the vet said, “It’s early. We don’t need to do anything right now. If he starts showing signs, there are medicines we can give him.”

So what is a heart murmur?

A heart murmur is an unusual sound in the heart caused by turbulence as blood flows through the dog’s heart.  Some are so soft they can only be heard through a stethoscope; others so loud,  you can feel them when you put your hand on the dog’s ribs.

What causes a dog heart murmur?

A variety of things can cause a dog heart murmur, some more easily treated than others. If a dog has too little iron (anemia) or too little protein (malnutrition) in its blood, the blood may be too watery and so cause the murmuring sound. Leaky valves, narrowed arteries or heart muscle problems may cause the blood to not flow smoothly through the heart.

Some of these conditions may exist from birth; others develop as a dog ages or develops other health issues. These include too much of the hormone thyroid, heart worms, a fever, an infection or being pregnant or obese can also cause a dog’s heart to murmur.

There may be a genetic aspect as well. Small breed dogs such as Yorkshire terriers, dachshunds, shih tzu, Pomeranians or Chihuahuas are prone to getting leaking mitral valves as they age. Certain larger breeds such as boxers, cocker spaniels and cavalier King Charles spaniels also develop heart murmurs more often than other breeds. Mixed breed dogs are not immune either.

Usually, you don’t notice any symptoms, until your vet picks it up during a physical exam. Depending on how severe it is and whether it is affecting the dog’s life, a vet may order more tests. The same tools used to diagnose heart conditions in humans can be used to do so in dogs, including:

• Blood tests.
• Chest X-rays.
• Electrodardiograms.
• Echocardiograms and Doppler exams, which can measure the speed and direction of blood flow across heart valves and in its chambers. An echocardiogram lets a vet see the size and movement of the heart.

As a dog ages or the conditions causing the heart murmur get worse, your dog may:

• Develop a cough, especially during or after lying down for awhile.
• Have difficulties breathing.
• Be tired and not willing to walk distances or play hard.
• Collapse or have fainting spells.
• Lose his appetite and start losing weight.

How can it be treated?

In many cases, no treatment is required. Some puppies even outgrow heart murmurs. If a vet finds a treatable condition —  anemia, a thyroid imbalance, malnutrition or obesity — that condition is treated and the heart murmur may go away. Even if the murmur is the result of a heart condition, medicines, exercise and a change of diet may be all that is needed to keep the dog living well.

While a heart murmur can’t always be cured, it is not the end of the line for Fido. Knowing the signs of a worsening condition in the bullet points above helps you be watchful and bring in a vet’s expertise when needed.