A heart murmur occurs whenever there is turbulence in the blood flow when the heart contracts. The most common times this occurs is when a pet has defect in a heart valve which allows blood to leak back into the atrium when the hearts main chambers, the ventricles, contract. They can, however occur in other circumstances such as anaemia because the blood is thinner and so flows differently. Some animals will have murmurs caused by the way their heart is positioned in the chest and these may never cause them any problems.

If a pet has a heart murmur as the result of a leaking heart valve it is quite likely that the heart will eventually develop heart disease and eventually heart failure. The rate that this change can happen varies tremendously from individual to individual. Basically, the leakage back of blood with each pump means the heart has to work harder to pump the same amount of blood. Over time the heart size and shape changes. First the atrium become larger because of the stretching of its walls by the regurgitated blood. The heart senses it is pumping less blood so it triggers the body to constrict blood vessels. It probably does this because it can't differentiate between acute blood loss, where constricting blood vessels is very helpful, and heart disease where constriction of the blood vessels means it is much harder for the heart to pump blood through the blood vessels. Because it has a harder time pumping against the constricted blood vessels the heart slowly enlarges in an effort to compensate for the changes. Unfortunately as it becomes larger, it becomes less efficient which further exacerbates the problems. Eventually the heart is functioning so poorly that fluid starts to build up, usually in the lungs, causing initially a cough and then difficulty in breathing, exercise intolerance among other things.

What we do depends on what stage the disease is in. It is very important to investigate what is happening so we can institute appropriate treatment at the appropriate stage. Waiting till heart disease becomes clinically obvious is the worst thing we can do when we find a murmur.

If the pet is a puppy and clinically doing great the murmur has a very good chance of disappearing as it grows so we will likely want to just recheck how it sounds every few months.

If it is a mature animal who has developed a murmur then we should do a chest x-ray to assess the size of the heart. If there is no heart enlargement and no clinical signs, Great! no treatment is presently needed. We may then reschedule a recheck in 6 months and depending if the sound of the murmur has changed we may repeat the x-ray or wait another 6 months.

If the heart is showing enlargement then we need to start medications. Typically we start with drugs that dilate the blood vessels so the heart doesn't have to pump against as much resistance. As time goes on other drugs become indicated including diuretics. If the heart is significantly enlarged we may also do ultrasound on the heart to assess its function and also an ECG.

Murmurs and heart disease must be monitored if we are to prevent the onset of heart failure any earlier than necessary.

Until clinical signs of heart disease occur one should treat their animals as if nothing was wrong at all. Remember the rate of change with heart murmurs can be very slow and some individuals never develop problems. We just don't know who those ones are so we need to monitor all pets with murmurs

The answer is almost always yes. Today's anaesthetics are extremely safe, even for those animals in clinical heart failure. All animals having an anaesthesia ideally should have some pre-anasthetic work-up in the form a chest x-ray and some blood tests.