Causes of Canine Heart Murmurs
Heart murmurs can be congenital (the dog is born with the condition) or acquired later in life. Murmurs can be caused by anatomical heart defects and by a number of infectious, inflammatory or other disease processes. Any of the heart valves (mitral, tricuspid, pulmonic, aortic) can be associated with heart murmurs. These valves can be affected by endocardiosis, endocarditis, valvular stenosis or dysplasia, with characteristic heart murmurs accompanying each condition.
Endocardiosis is a common cause of canine cardiac disease and is characterized by chronic thickening of the free edges of the heart valves, causing anything from minor leakage to severe malfunction. Endocarditis is an inflammatory change of the tissues lining the heart chambers and valves. Stenosis is a narrowing or constriction of a body passageway (such as an artery or vein) that causes increased turbulence at the affected area. Dysplasia simply means an abnormality of development, such as some alteration in size, shape, organization or structure. Characteristic murmurs usually accompany each of these conditions and can be detected by skilled veterinarians through auscultation, when listening to amplified heart sounds through a stethoscope.
Other causes of heart murmurs include atrial or ventricular septal defects (basically, a hole or tear in the interior wall separating the heart chambers); patent ductus arteriosus (a failure to close of an important blood passageway in the fetal heart); cardiomyopathy (primary disease of the heart muscle); heartworm infection (a serious parasitic disease); Tetralogy of Fallot (a congenital heart defect that combines four distinct structural anomalies); hyperthyroidism; and anemia, among others.
Preventing Heart Murmurs
A heart murmur is a clinical finding that cannot be prevented in the normal sense of that term. The underlying cause of the murmur must be found for resolution to be possible. Many heart murmurs will never require medical or surgical management, even if they are very pronounced. Minor murmurs can often be managed with exercise and/or dietary change. Surgical procedures may be available for dogs with more serious heart conditions causing their murmurs. Again, the murmur itself is not preventable or treatable. It is simply a sound that a veterinarian can detect when listening to the heart sounds during a physical examination.
If a veterinarian detects a heart murmur, she will likely recommend advanced diagnostic testing through use of an electrocardiogram (an EKG/ECG). The dog may be referred to a veterinary cardiology specialist to perform this testing. The prognosis for dogs with heart murmurs depends almost entirely on the nature and severity of the underlying cause of the condition. A murmur, by itself, is not necessarily a reflection of any illness or disease.