What it is
Before birth a puppy gets its oxygen from its mother, so its lungs are not yet in use and the ductus lets blood skip them. Once the puppy starts breathing, the vessel is meant to tighten and seal within days. When it stays open, blood is pushed from the aorta, the body's main artery, back into the lungs, returns to the left side of the heart and goes round the same loop again. That side of the heart ends up pumping far more blood than it should and stretches under the load.
It is a defect present from birth and can be inherited. The murmur it makes is continuous, like humming machinery, and a vet can hear it at the first puppy check, sometimes before any other sign appears.
If you are bringing home a new puppy, that first vet visit matters. Until a vet has looked into a murmur, let the puppy play at its own pace rather than taking it on long walks or rough games.
Signs you may notice
- Grows slower than littermates
- Tires quickly during play
- Breathes fast or with effort
- Coughs after activity
A puppy may grow more slowly than its littermates, tire quickly during play or breathe with more effort, though some seem perfectly healthy at first. Coughing or breathlessness after exercise is a reason to talk to a vet.
When to see a vet
Book a visit if your puppy tires easily, grows slowly or coughs, and make sure every new puppy has its heart listened to. Struggling to breathe or collapse means a vet is needed immediately.
This is general information, not veterinary advice. For your own dog's health, tests and treatment, see a vet.