Rock Falls, IL
A continuous murmur is a heart sound. It is not normal, but it does not always signify a serious problem.
Heart murmurs come in many varieties. Systolic murmurs and continuous murmurs are the most common. Heart murmurs of all types occur when blood flows through the heart in a turbulent fashion. Continuous murmurs are not necessarily more dangerous than systolic (or other) murmurs.
Under normal circumstances, blood flows through the heart in a smooth (or laminar) fashion. When something disrupts the smooth flow of blood, a shooshing sound will occur. The principle is the same as kinking a hose and hearing the water rush through the kink.
Some heart murmurs are caused by harmless problems. Others indicate leaking valves or other potentially serious issues. Unfortunately, in an 11-year-old dog a leaking valve is the most likely cause of a newly acquired murmur.
Kristine, diagnostic imaging (X-rays and ultrasound) is the only way to determine whether your dog’s murmur is a problem. I recommend that you talk to your vet about this. If a leaking valve or other issue is found then medications may be available to prevent complications from the syndrome.