🫀 Subaortic Stenosis in Dogs: A 2025 Vet Guide to Diagnosis and Management 🐶

By Dr Duncan Houston, BVSc

Subaortic stenosis (SAS) is a congenital heart defect where a scar-like narrowing (stenosis) develops below the aortic valve, restricting blood flow from the heart to the body. This condition can lead to heart murmurs, electrical disturbances, fainting, and even sudden death. Early diagnosis and lifelong management are essential to helping dogs with SAS live longer, healthier lives. 🩺🐾

🧬 What Is Subaortic Stenosis?

In a normal heart, blood is pumped from the left ventricle through the left ventricular outflow tract (LVOT) and across the aortic valve into the aorta — the main artery supplying the body. In SAS, a fibrous ridge or ring of tissue forms just below the valve, narrowing this outflow tract. ⛓️

This narrowing causes:

• 💨 Turbulent blood flow = heart murmur
• 🧱 Extra work for the heart = muscle thickening (hypertrophy)
• ⚡ Disrupted electrical signals = risk of arrhythmia and sudden death

🐕 Breeds at Risk

SAS is genetic and seen most often in:

• Golden Retriever
• Newfoundland
• Rottweiler
• Boxer
• German Shepherd
• Great Dane
• Dogue de Bordeaux
• German Shorthaired Pointer

❗ No dog with SAS, even mild cases, should be bred due to unpredictable inheritance. 🧬

👂 Recognizing a Heart Murmur

The first sign of SAS is often a heart murmur, heard during a routine puppy exam. Murmurs are caused by turbulent blood flow through the narrowed valve area. 🎧

📍 SAS murmurs are typically:

• 📈 Louder over time (as the stenosis worsens)
• 📍 Best heard at the base of the heart (left side of the chest)
• 🔊 Radiates up the neck (carotid arteries)

🚨 Innocent Murmur or SAS?

Some puppies have innocent murmurs that disappear by 6 months of age. If a murmur persists beyond that — or grows louder — further testing is needed. 🩺

🧪 Diagnosis of SAS

🔍 A combination of tests helps confirm SAS:

• 📸 Chest X-rays: Check for aortic bulge or signs of heart enlargement
• 🫀 Echocardiogram (ultrasound): Essential for measuring chamber size, wall thickness, and flow obstruction
• 📊 Doppler study: Measures pressure gradient across the stenosis

Pressure levels guide severity:

• 🌿 Mild: < 40 mmHg
• ⚠️ Moderate: 40–80 mmHg
• 🚨 Severe: > 80 mmHg

🔁 Mild cases may need monitoring only. Moderate to severe cases require lifelong management.

💊 Treatment Options for SAS

1️⃣ Beta Blockers (e.g. Atenolol)

These medications slow the heart rate, reduce stress on the heart muscle, and lower the risk of dangerous arrhythmias. 📉

📈 In one study, dogs on atenolol had a median survival of 56 months compared to 19 months with no treatment.

2️⃣ Exercise Restriction

Because fatal arrhythmias often occur during or after exertion, exercise should be controlled:

• ⛔ No intense play or running
• ✅ Gentle walks and enrichment are okay

🎯 Avoid excitement or overheating. Sudden death can happen without warning, especially in young, active dogs.

3️⃣ Surgery

Open heart surgery can remove the fibrous ridge — but is rarely performed due to cost, risk, and minimal improvement in outcomes. 🩻

4️⃣ Balloon Valvuloplasty

This catheter-based procedure attempts to dilate the stenosis with an inflatable balloon. While it sounds promising, survival times are similar to medication alone. 💔

🔬 More studies are needed before invasive options become preferred over medication.

📉 Prognosis

• 🟢 Mild SAS: May live a full life without treatment
• 🟡 Moderate SAS: Needs management, can live years
• 🔴 Severe SAS: Higher risk of early death, sudden collapse, arrhythmias

📱 Monitoring at Home with Ask A Vet

If your dog is diagnosed with SAS, it’s important to monitor for symptoms and track medication. The Ask A Vet App helps you:

• 📊 Track atenolol dosing and heart rate
• 📅 Log symptoms like fainting, fatigue, or coughing
• 💬 Connect with licensed veterinarians for support

Visit AskAVet.com to start supporting your dog’s heart health. ❤️

🧠 Final Thoughts from Dr Duncan Houston

Subaortic stenosis is a serious but manageable heart condition in dogs. With early diagnosis, beta blockers, and careful lifestyle adjustments, many dogs can live long, quality lives. 🐾

Recognize murmurs early. Work with your vet closely. And never hesitate to seek help from Ask A Vet if your dog shows signs of fatigue, collapse, or distress. 🫀🐶