A heart murmur is caused by vibrations in the heart. or blood vessels.
These vibrations are usually created by turbulence, and occasionally by
vibrations of structures in the heart e.g, valves, Just imagine a. river
flowing slowly and smoothly, that is laminar flow, Now picture a small
fast-flowing stream with lots of currents and eddies, this is turbulent
Turbulence is due to one of three things:
Each heart beat ejects a certain volume of blood, the stroke volume, Puppies
have larger stroke volumes for their size than adult dogs. This means
that for each heart beat, a relatively larger volume of blood is ejected
out a smaller vessel when compared to an adult dog. When excited such
as at a veterinary surgery, this can increase further and so the outflow
velocity from the ventricles in the aorta or pulmonary artery can increase
above a certain threshold and become turbulent creating a murmur.
- High velocity blood flow
- Low blood viscosity - as seen in anaemia
- Flow from a narrow region into a large area
Typically these innocent flow murmurs tend to be fairly quiet (up to grade
3), soft and blowing in character and occur at the beginning to middle
of the heart heat, Also they are usually loudest over the aorta or pulmonary
artery and can vary with body position. Unfortunately, it is impossible
to differentiate between some mild congenital heart diseases such as sub-aortic
stenosis (a narrowing under the valves at the base of the aorta) and a
flow murmur. Most importantly, innocent flow murmurs disappear by 6 months
If you have a puppy with a murmur that could be a flow murmur, you have
Hence, if I pick up a quiet murmur in a young puppy at a show, I would
recommend that the owner waits to see how it develops before making any
drastic decisions. If it is an innocent flow murmur, it should gradually
get quieter and disappear. Anything more significant will persist and
require further investigation.
- Have the puppy re-examined in 1 month. An innocent flow murmur should
get quieter as the puppy grows. If the murmur is the same or louder,
further investigations such as Doppler ultrasound examination would
- Have a Doppler ultrasound examination performed if you need to know
NOW. This will allow the cardiologist to assess the valves and the
speed and direction of blood flow through the heart can be measured.
This will differentiate between mild heart disease and flow murmurs.