Heart Problems in Australian Shepherds

Subvalvular aortic stenosis is a ring of extra fibrous tissue that forms just below the aortic valve during heart development, narrowing the space blood has to pass through on its way out to the body. It isn't caused by anything that happens after birth — it's a developmental variation that's already present the day a puppy is born, even though it usually isn't detected until a stethoscope picks up the resulting murmur weeks or months later.

The severity varies enormously. A mild narrowing may never cause a noticeable problem in the dog's entire life. A more significant one forces the heart's left side to work much harder than normal for years, which over time can lead to thickening of the heart muscle and, in serious cases, a risk of sudden collapse during exertion. That range — from clinically invisible to serious — is exactly why every case gets its own full workup rather than a one-size-fits-all answer.

Because this is congenital, it's typically first suspected young — at a puppy exam, a pre-purchase veterinary check, or occasionally not until a young adult dog gets its first thorough listen during a spay or neuter pre-anesthetic exam. A murmur at that stage prompts a referral to a veterinary cardiologist for an echocardiogram, which is the only way to actually measure how narrow the passage is and how hard the heart is compensating.

Once measured, dogs are typically placed into a mild, moderate, or severe category, each with a different monitoring schedule and a different realistic outlook. Mild cases are often followed with periodic rechecks and otherwise live an entirely normal life; moderate and severe cases need closer, ongoing cardiology involvement and more conservative guidance around strenuous exercise.

If you think your Aussie has heart problems, the plan is three steps: write down what you have seen and when it started, book a veterinary appointment rather than waiting for the next flare, and take video of the behaviour or symptom before you go — the thing you are worried about rarely happens in the consulting room. Screening in the parents covers hip dysplasia, elbow dysplasia, epilepsy.

What the vet visit should produce is a diagnosis and a written plan, not just reassurance: what is being ruled out, what the monitoring interval is, and which signs mean you come back sooner. Ask what the treatment costs across a year rather than per visit, because that is the number that decides whether you are managing this condition or reacting to it.

Between appointments, keep a short log — dates, what you saw, what changed. It is the single most useful thing an owner brings to a follow-up, and for heart problems it is often what separates a clear pattern from a guess.