The most common cause of an acquired heart murmur in the dog is 'mitral insufficiency' (also called 'mitral regurgitation'), a condition in which the mitral valve becomes thickened and begins leaking (see our handout 'Mitral Valve Disease in Dogs') - mitral insufficiency tends to be more common in small breed dogs.
Why would a dog develop a heart murmur?
Most commonly, heart murmurs in small dogs are caused by a leaky mitral valve (the heart valve in between the left atrium and left ventricle). The mitral valve allows blood to flow from the left atrium to the left ventricle but does not allow for blood to flow back into the left atrium.
When should I worry about a heart murmur in my dog?
Loud heart murmurs (Grade 3-4/6 to 6/6) in a new puppy or kitty and soft heart murmurs that persist beyond 14-16 weeks of age should be evaluated by a cardiologist. This may indicate that congenital (present at birth) heart disease is present.
Can dogs develop a heart murmur later in life?
Congenital Murmurs Some animals are born with a congenital heart murmur, due to structural defects within the heart. Usually, these murmurs are found during puppy and kitten exams. Sometimes these murmurs can only be detected later in life. The severity and causes of congenital murmurs vary widely.
Is a heart murmur in a dog fatal?
Is my dog in heart failure? Heart murmurs with pathological heart diseases usually progress into congestive heart failure. This is a serious condition and can be fatal. Commonly, dogs that are in heart failure will have an accumulation of fluids in their lungs.