A heart murmur in a dog is an unexpected sound detected during a cardiac examination, signaling turbulent blood flow within the heart. This symptom requires veterinary attention to determine its significance, as some murmurs are benign while others indicate underlying heart conditions. Identifying the cause is important for appropriate care.
What is a Heart Murmur?
A heart murmur is the sound produced by abnormal blood flow within the heart, identified by veterinarians using a stethoscope. Instead of the usual “lub-dub” sound of a healthy heartbeat, a murmur presents as a “whoosh” or “shoosh” sound. This turbulent flow can change or muffle normal heartbeat sounds.
Veterinarians classify murmurs using a grading system from Grade I to VI, based on intensity. A Grade I murmur is very soft and might only be heard intermittently, while a Grade VI murmur is exceptionally loud and can even be felt. While a louder murmur can indicate more advanced disease, intensity does not always directly correlate with severity.
Murmurs are also characterized by their timing within the heart cycle (systolic, diastolic, or continuous) and their loudest location. Some are “innocent” or “physiological,” meaning they have no adverse impact on health and often resolve, especially in young puppies. Pathological murmurs are caused by an underlying structural heart issue or other medical problems.
Causes of Heart Murmurs in Dogs
Heart murmurs in dogs can stem from various underlying issues, ranging from birth defects to acquired conditions. These causes generally lead to turbulent blood flow, which creates the audible murmur. Identifying the specific cause is important for determining the appropriate course of action.
Congenital defects are abnormalities present at birth that can disrupt normal blood flow. Common examples include Patent Ductus Arteriosus (PDA), where a blood vessel remains open after birth, and Pulmonic or Aortic Stenosis, a narrowing of heart vessels. Ventricular Septal Defects (VSDs), or holes between heart chambers, also cause turbulence.
Acquired heart diseases are a frequent cause of murmurs, particularly in older dogs. Degenerative Mitral Valve Disease (DMVD) is common in small breeds, occurring when the mitral valve thickens and leaks. Dilated Cardiomyopathy (DCM), often seen in larger breeds, involves weakened heart muscle, leading to reduced pumping efficiency and potential valve leakage.
Other non-cardiac conditions can also induce murmurs by altering blood flow dynamics. Anemia, fever, or hyperthyroidism can increase blood flow velocity and reduce blood viscosity, leading to turbulence. These typically result in physiological murmurs that may resolve once the underlying issue is addressed.
Diagnosing and Managing a Heart Murmur
Diagnosing a heart murmur involves a thorough veterinary examination and diagnostic tests. After detection, the veterinarian considers its grade, location, and timing to narrow potential causes. This initial assessment guides further investigation into the dog’s cardiac health.
Diagnostic steps include chest X-rays, which provide images of the heart’s size and shape, and check for fluid accumulation in the lungs. An electrocardiogram (ECG) measures the heart’s electrical activity, detecting abnormal rhythms. An echocardiogram, an ultrasound of the heart, is the most definitive diagnostic tool, visualizing heart structure, valve function, and blood flow patterns.
Management strategies for a heart murmur depend on its underlying cause and severity. For innocent murmurs, particularly in puppies, no treatment may be required beyond regular monitoring to ensure they resolve. For pathological murmurs, treatment can involve medication to improve heart function, dietary adjustments, and in some cases, surgical correction for specific congenital defects like PDA or pulmonic stenosis. Medications might include diuretics, ACE inhibitors, or inodilators to enhance heart muscle pumping.
Prognosis and Living with a Dog with a Murmur
The prognosis for a dog with a heart murmur varies significantly depending on its underlying cause, severity, and response to treatment. For dogs with innocent murmurs, the outlook is generally excellent, as these often disappear on their own. If the murmur is due to a treatable extracardiac issue, the prognosis is also favorable once resolved.
For murmurs caused by congenital heart defects, the prognosis is highly variable; surgically corrected defects often have a good outcome. Acquired heart diseases, such as degenerative mitral valve disease, can often be managed with long-term medications to maintain quality of life, though they are progressive. The prognosis for conditions like dilated cardiomyopathy can be more guarded, especially if the dog is already showing signs of heart failure.
Owners play a crucial role in managing a dog with a heart murmur through careful monitoring and adherence to veterinary recommendations. This includes regular check-ups, which may involve repeat echocardiograms and X-rays, to track the murmur’s progression and heart health. Lifestyle adjustments, such as controlled exercise and specialized diets, might be necessary. Owners should also watch for signs of worsening heart disease, including coughing, increased resting respiratory rate, lethargy, difficulty breathing, or fainting spells, and report them promptly.