Vet Guide to Heart Septal Defects in Dogs 2025 🐶🩺 

By Dr. Duncan Houston BVSc

Heart septal defects are congenital holes in the septum between heart chambers: atrial septal defect (ASD) in the atria or ventricular septal defect (VSD) in the ventricles. These allow abnormal blood flow (shunts) leading to volume overload, murmurs, and, in severe cases, heart failure.

📍 Types & Causes

• ASD: Hole in interatrial septum (ostium primum, secundum, or sinus venosus). Shunting is usually from left to right, overloading the right heart and lungs, possibly causing pulmonary hypertension or, with chronic pressure, reversal and cyanosis.
• VSD: A hole in the ventricular septum, most commonly perimembranous, causing left-to-right shunting. Smaller defects may close spontaneously; large defects can produce volume overload and pulmonary hypertension.

⚠️ Clinical Signs

• Heart murmur: ASD often causes a soft systolic ejection murmur; VSD produces a loud holo-/pansystolic murmur over the right chest.
• Exercise intolerance, coughing, respiratory signs, fainting, cyanosis, ascites in advanced cases.
• Small defects may be asymptomatic and have an excellent prognosis.

🔬 Diagnosis

• Clinical exam: Auscultation reveals characteristic murmurs.
• Chest X-ray & ECG: Assess chamber enlargement and pulmonary vasculature.
• Echocardiography with Doppler: Gold standard for diagnosis: identifies defects, shunt direction, chamber dilation, and pulmonary pressures.

💊 Treatment & Management

• Small ASD/VSD: Often monitored; may close spontaneously; excellent prognosis.
• Moderate to large defects: Medical therapy with diuretics, vasodilators, and ACE inhibitors; restricted exercise.
• Surgical/interventional closure: Rare but possible in specialized centers; usually for significant lesions.
• Reversal (Eisenmenger’s): Open-heart surgery contraindicated; management is supportive (oxygen, phlebotomy), and prognosis is guarded.

📈 Prognosis & Monitoring

• Small defects: normal life expectancy.
• Moderate/large defects: require lifelong monitoring; early intervention improves outcomes.
• Symptoms to monitor: exercise tolerance, breathing rate, gum color, body condition, and weight.

✅ Vet Tips by Dr Duncan Houston BVSc

• 🔍 Investigate any murmur—early echo determines defect size and management plan.
• 📆 Repeat echocardiograms every 6–12 months for moderate/large defects to track changes.
• 💡 Begin medical therapy before signs of heart failure develop.
• 💬 Discuss specialized surgical options with a canine cardiologist for eligible cases.
• 🚫 Recommend against breeding affected dogs—heart septal defects are hereditary.

If your dog has a heart murmur, especially if it leads to tiredness, coughing, breathing difficulty, fainting, or bluish gums, seek veterinary assessment immediately. Use the AskAVet.com app for remote cardiology advice, 🐾❤️