Definition of Heart Murmurs
A heart murmur is simply an abnormal heart sound caused by turbulent blood flow. Having a heart murmur is not itself an illness or disease, but instead is a consequence of something else causing the audible heart sounds to be abnormal.
How Heart Murmurs Affect Dogs
Many dogs show no apparent signs of heart murmurs, which often are only detected during a routine check-up. When heart murmurs do accompany clinical signs, generally there is something more serious going on with the animal’s heart and the murmur is a consequence of that underlying condition. The signs of heart disease are nonspecific. Some dogs will become intolerant to exercise or just generally “slow down.” They may pant while resting and seem to have difficulty breathing. Their mucous membranes may become pale. The dog may cough and appear “pot-bellied” from fluid retention. Puppies commonly have benign heart murmurs which disappear by roughly 6 months of age.
Causes of Canine Heart Murmurs
Heart murmurs can be congenital or acquired and can be caused by many different structural heart defects as well as by a number of infectious and other processes. Any of the heart valves (mitral, tricuspid, pulmonic, aortic) can be affected by endocardiosis, endocarditis, valvular stenosis or dysplasia, with characteristic heart sounds accompanying each. Endocardiosis is a common cause of canine cardiac disease and is characterized by chronic fibrosis and thickening of the free valve edges, 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 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 with their stethoscope. Other causes of murmurs include atrial and ventricular septal defects (basically, a hole or tear of the interior wall separating the heart chambers); patent ductus arteriosus (a failure to close of an important duct in the fetal heart); cardiomyopathy (primary disease of the heart muscle); heartworm infection; Tetralogy of Fallot (a congenital heart defect that combines four distinct structural anomalies); hyperthyroidism; and anemia, among others.
Prevention of Heart Murmurs in Dogs
Murmurs are a clinical finding that cannot be “prevented” in the normal sense of that term. The underlying cause of the murmur must be found. 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.
Special Notes
If your veterinarian detects a murmur in your dog, she will likely recommend advanced diagnostics through use of an electrocardiograph (an EKG). You 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.