What Causes Heart Murmur in Dogs?

Your dog has just been diagnosed with a canine heart murmur and you're devastated. You wonder how could this happen without you realizing something was wrong. Questions race through your head and you don't hear another word your veterinarian says because you're busy panicking. While it is a serious diagnosis, with a little medication and some common sense your dog could live her life without problems.



A heart murmur in dogs is an abnormal sound that indicates a turbulent blood flow through the heart. Veterinarians characterize the level of heart murmur on a scale from 1 to 6 depending on the loudness and location of the sounds in the heart, the time during the heart's cycle when the sounds occur and whether they are short or long. Grade 1 is barely audible, while grade 6 is very loud and you can feel the vibration by touching your pet's chest. A heart murmur itself is not an illness, but it could indicate the dog suffers from a condition that affects her heart.


Dogs develop different types of canine heart murmurs depending on the cause, which veterinarians typically classify as systolic or diastolic. Young puppies commonly have soft-sounding heart murmurs, which are often innocent or benign murmurs and are not indications of heart disease. These usually clear up by around 4 months of age. Congenital murmurs exist from birth, while acquired murmurs develop during the pet's lifetime. Although both of these types of murmurs can be benign, congenital murmurs can lead to complications while acquired murmurs frequently indicate developing heart disease.


Heart murmurs in dogs could indicate structural heart problems caused by abnormal, diseased or incompetent valves or structures vibrating in the blood flow. Reasons for abnormalities include low levels of red blood cells or protein, a leaking mitral valve, a bacterial endocarditis infection and obesity. Systolic murmurs can be caused by conditions such as anemia, hyperthyroidism, heartworm disease, heart failure, valve disease, among others. The blood flow may be obstructed or the dog could have a defect in the wall separating the two sides of the heart.


Certain breeds of dogs are more likely to develop acquired heart murmurs than others. Small breeds such as Chihuahuas and Yorkshire terriers are prone to developing degenerative mitral valve heart disease when they get older, while boxers and cavalier King Charles spaniels have high statistics for the prevalence of the disease.

Diagnosis and Treatment

Heart murmurs typically don't produce symptoms. Veterinarians diagnose the condition based on listening to the dog's heart during a routine examination, or when the dog shows symptoms associated with other illnesses. Symptoms include persistent coughing, fatigue, poor appetite and weight loss, breathing problems, low tolerance for exercise, collapsing or fainting spells. The murmur itself is not treatable, but the veterinarian treats the underlying condition that is causing it according to prescribed methods.

By Tracey Sandilands

About the Author
Tracey Sandilands has written professionally since 1990, covering business, home ownership and pets. She holds a professional business management qualification, a bachelor's degree in communications and a diploma in public relations and journalism. Sandilands is the former editor of an international property news portal and an experienced dog breeder and trainer.