Newfoundland Heart Murmurs: What the Sound Actually Means

Veterinarians grade murmurs on a scale from one to six. A grade one is so quiet it takes a silent room and a patient listener to find. A grade six is loud enough to feel through the chest wall as a vibration. It is natural to read that scale as a severity ranking, and that reading is wrong often enough to be worth correcting.

Loudness reflects how much turbulence is being created, which depends on the shape of the abnormality and the speed of the blood moving through it. A small, tight narrowing can be very noisy. A badly failing heart can be relatively quiet because it is no longer moving blood forcefully enough to make much sound. Grade tells your veterinarian how confident to be that something structural is there. It does not tell anyone how sick the dog is.

Where the sound is loudest is more informative than how loud it is. A murmur best heard high on the left side of the chest points toward the outflow tract from the left ventricle, which in a Newfoundland raises the possibility of the subaortic narrowing documented in the breed. That is the specific reason an unexplained murmur in this breed usually earns an ultrasound rather than a shrug.

Growing puppies of all breeds can produce soft murmurs that mean nothing at all. Blood moving quickly through a small, rapidly changing body sometimes makes noise without any defect being present, and these innocent murmurs typically fade as the puppy grows.

That fact is genuinely reassuring in most breeds. In a Newfoundland it creates a trap, because the breed's characteristic congenital defect is also present in puppies, also produces a murmur, and can also be soft early on. Waiting to see whether the noise disappears is a reasonable plan only if somebody has decided, deliberately, that this particular murmur has the character of an innocent one and has set a firm date to listen again.

The practical version of this is simple. If your Newfoundland puppy has a murmur, ask two questions before you leave: what would make you concerned about this specific murmur, and when exactly do you want to hear it again? An unbooked recheck is the most common way a real defect gets discovered late.

One more note for puppy buyers. If a litter has been examined by a cardiologist, ask which puppies were examined and at what age, because a murmur that develops after the litter went home would not appear on that paperwork at all.

None of this is painful and most of it happens in a single appointment. What you are paying for is a name for the sound and a number that makes future comparison possible.