Heart Murmurs in Dogs

Say you went into the clinic for a physical exam and vaccinations, and you were told your dog has a heart murmur. What does this mean? A heart murmur is an abnormal sound heard when listening to the heartbeat. Instead of the normal “lub dub” sound, you will hear a “woosh dub”.

The most common reason for this is a leaky heart valve (mitral valve or aortic valve) and the mitral valve which is on the left side of the heart is the most common type. There are other reasons for a murmur besides a leaky valve: anemia and thinner blood can create turbulence and a murmur; holes in the heart wall such as with young dogs with inherited heart defects; changes in heart shape and contractility from heart muscle diseases. Certain breeds have a higher risk of heart murmurs such as the Cavalier King Charles Spaniel, Toy and Miniature Poodle, Schnauzer, Shih Tzu, Cocker Spaniel, and other breeds under 25 pounds (adult weight) – these are usually due to changes in the valve leaflets due to breed genetics and age. Large breeds with murmurs more often have heart muscle diseases and not valve changes, and starting a cardiac work-up is recommended and their diseases and risks will be covered in another article.

If your dog is otherwise healthy and there is no history of coughing or exercise intolerance, it is not likely the heart murmur is causing a problem yet, so we have some time to do a work-up. We would recommend chest xrays to evaluate the heart size and shape and Vertebral Heart Score (VHS).

This gives us a baseline to compare with x-rays in the future. The VHS helps us see if the heart is enlarging in response to the leaky valve, which lets us know it is time to start medications to help the heart contract better before heart failure starts. Many small breed dogs with heart murmurs develop congestive heart failure (CHF) over time, so yearly or twice a year exams and yearly x-rays are recommended. Some dogs need to have a cardiac ultrasound (echo) and EKG and blood pressure in addition to radiographs. Signs of CHF are coughing, breathing rate at rest >40 breaths per minute, gum or tongue color changes from pink (normal) to violet (abnormal), and exercise intolerance.

If your dog has been coughing and you brought him into the clinic and we found a heart murmur, we would recommend chest x-rays right away. Radiographs will show if there is fluid in the lungs (pulmonary edema) from congestive heart failure and we will measure VHS and look for heart enlargement. Some dogs with heart murmurs and a cough do not have congestive heart failure – they can have respiratory problems such as bronchitis, pneumonia, collapsing trachea, kennel cough, or cancer. Respiratory problems are treated differently than heart problems. There are good medications for dogs with CHF, including therapy with pimobendan, enalapril, and furosemide. An additional medication called spironolactone is added for some patients. With CHF, recheck x-rays and exams are needed to monitor response to treatment and blood tests are done to see if kidney function is being impacted by the medications. Staying in the hospital in an oxygen cage is necessary for patients with low oxygenation of the blood (pulse ox) along with fluid in the lungs (pulmonary edema). An exam by a board-certified cardiologist and an echocardiogram is needed in some cases.

In summary, we recommend x-rays for all dogs with heart murmurs. With proper monitoring and medications, our canine friends can live longer, happier lives.