What is a heart murmur?

A murmur is a sound produced by flow of blood inside the heart when it pumps. There are many causes of a murmur. Some are simply caused by normal blood flow, but others can be associated with heart disease.

Hearing your vet say that “your pet has a heart murmur” can be very daunting. The significance of a murmur depends upon the cause – some heart disease that cause loud murmurs may not require any treatment at all. Others will lead to a problem for the affected dog or cat without treatment. From listening alone, it is almost impossible to tell the difference.

Innocent heart murmurs

Puppies and kittens less than 6-months old can have innocent or benign murmurs. These occur due the fast flow of blood in such a small heart. As they grow and their heart grows and matures, then the murmur gradually disappears.

Murmurs due to regurgitation

Each of the four valves in the heart act as non-return valves, permitting only forwards blood flow. If a valve becomes faulty and no longer prevents backflow, then the resulting backward squirt of blood through the gaps in the valve cause a sound that we call a murmur.

Murmurs due to narrowed valves

If a heart valve is abnormally narrowed, usually due to a congenital defect, then blood flow pumped out through the narrowed valve is pinched, resulting in an abnormal squirt of flow. This can be likened to putting a thumb over the end of a hose pipe to make the water squirt, rather than pour.

Murmurs due to ‘holes in the heart’ or a patent ductus arteriosus (PDA)

A murmur can also occur through a hole in the heart – the murmur is caused by the squirt of blood going through the hole at high speed. An abnormal blood vessel remaining open after birth, called a PDA, can cause the same effect.

Murmurs associated with illness

A murmur can also be produced when a pet is anaemic and the blood is thin. In this situation, thinner blood results in faster speed of flow and thus a murmur. A similar situation can occur when a pet is ill for other reasons, such as during a fever.

What is the best way to diagnose a murmur?

Whether the defect causing the murmur is significant for your pet can be determined by an experienced cardiologist, often through performing an ultrasound scan of the heart. Some defects can be mild and have no effect on the heart and animals can live a full and normal life with them. If a heart problem is enough to require treatment, then a cardiology specialist can help review the best options with pet owners.

If you are concerned about a heart murmur, ask your vet to refer you to a registered Specialist in veterinary cardiology, who will listen to the murmur and decide what tests need to be done to reach a diagnosis and to assess the severity. Nearly always, an ultrasound scan is the best way to diagnose a murmur. Sometimes additional tests are also required, such as chest x-rays, an ECG or cardiac-specific blood tests. Echocardiography to accurately diagnose and stage heart disease is challenging, and is best performed by a Specialist in cardiology, using a high-specification ultrasound machine.

If you have any questions or concerns, please do not hesitate to contact us or speak to your primary care vet.