What is a heart murmur? A heart murmur is an abnormal heart sound, usually heard by listening to the heart with a stethoscope.
What causes a heart murmur? A heart murmur is caused by turbulent blood flow within the heart. Sometimes a murmur is determined to be 'innocent' or 'physiologic', while other times the murmur is determined to be pathologic or caused by disease. Pathologic heart murmurs can be caused by a structural problem within the heart (i.e., cardiac disease), or can be due to a problem that is 'extracardiac' (i.e., not caused by heart disease).
Do all murmurs sound the same? No. The loudness of a murmur reflects the amount of turbulence that is present in the heart. However, the loudness of a heart murmur does not always correlate directly with the severity of disease.
Murmurs are graded by their intensity, usually on a scale of I-VI. A Grade I murmur is very soft or quiet, may only be heard intermittently, and is usually only heard in one location on the chest, while a Grade VI murmur is very loud, heard everywhere that the heart can be heard, and can be felt when a person places their hand on the chest in the area of the heart (in cardiac terminology, this is called a 'thrill').
Murmurs are also characterized by the time in which they occur during the heart cycle, and by whether they are long or short. Most murmurs are also characterized by their location, or where they are the loudest. The majority of murmurs in the dog occur during systole, the phase of the heart cycle when the heart is contracting to pump blood out. The specific characteristics of the murmur, along with any symptoms that your dog might be showing, will help your veterinarian to determine what is causing the murmur.
What is an innocent or physiologic heart murmur?"An innocent or physiologic heart murmur is a heart murmur that has no impact on the dog's health."An innocent or physiologic heart murmur is a heart murmur that has no impact on the dog's health.
It is very common for young puppies, especially large breed puppies, to develop an innocent heart murmur while they are growing rapidly. The murmur may first appear at 6-8 weeks of age, and a puppy with an innocent heart murmur will usually outgrow it by about 4-5 months of age. This type of murmur is benign.
In general, a physiologic or innocent heart murmur will have a low intensity (usually Grade I-II out of VI), and does not cause any symptoms or clinical signs.
This information is provided through years of research and should be considered opinion and is not to take the place of your regular veterinary care.