What it is
With each heartbeat, the left ventricle pushes blood through the aortic valve into the aorta, the main artery to the body. In subaortic stenosis a ridge or ring of tissue sits just below that valve, like a narrowing in a pipe. The heart muscle must squeeze harder to force blood past it, so it thickens, and the fast, swirling jet of blood beyond the narrowing makes a murmur that a vet can hear.
The defect is inherited and present from birth, but the ridge can keep developing while a puppy grows, so a murmur may only become clear after the first months of life.
How much a dog can do depends on how tight the narrowing is, and your vet will advise on exercise. Fainting during hard play or excitement is the warning sign to know: it means the heart cannot keep up.
Signs you may notice
- Tires quickly during play
- Heavy breathing after exercise
- Faints when excited
- Sudden weakness or collapse
A mild form may cause no signs at all, while with a more severe one the dog tires quickly, breathes heavily after exercise or even faints during play. If the dog faints, it needs a vet immediately.
When to see a vet
If your dog faints or collapses, it needs a vet immediately. Tiring sooner than before, or heavy breathing after ordinary exercise, is worth booking a visit for.
This is general information, not veterinary advice. For your own dog's health, tests and treatment, see a vet.