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Is Your Puppy’s Heart Murmur a Ventricular Septal Defect? — Symptoms, Diagnosis, and Management

HeartQ&AMeongsiljang Veterinary Advisory Board

Ventricular septal defect (VSD) in puppies is a congenital heart disease where blood flows abnormally due to a hole in the wall between the heart's ventricles. Here’s a summary of the key information every pet owner should know.

What Is Ventricular Septal Defect in Puppies?

Anatomical diagram of a dog's heart showing a ventricular septal defect

Ventricular septal defect (VSD) in dogs is a relatively common congenital heart disease caused by a hole in the septum between the left and right ventricles, allowing abnormal blood flow between the two chambers. This defect occurs when the septum fails to close completely during fetal heart development and is typically present at birth. Small defects with restricted blood flow (restrictive VSDs) may place minimal strain on the heart, whereas larger defects can burden the heart, potentially leading to left-sided heart failure, respiratory distress, and growth retardation. Diagnosis is made by a veterinarian who detects an abnormal heart murmur during auscultation and confirms the defect’s location, size, and direction of blood flow using color Doppler echocardiography.

Why Does Ventricular Septal Defect Occur?

Ventricular septal defect occurs when the septum between the ventricles fails to form completely during fetal heart development, and it is known to have a genetic predisposition. For example, early genetic studies in Keeshonds have shown that conotruncal malformations are associated with defects in a single autosomal gene locus. Additionally, a predisposition has been reported in large-breed dogs. However, since the exact causes, including breed-specific incidence trends and environmental factors during pregnancy, have not yet been fully elucidated, it is advisable to consult with a veterinarian for evaluation rather than making definitive conclusions. If a genetic predisposition is suspected, it is prudent to consider the associated risks when planning breeding.

A view of the ventricular septum failing to close properly during fetal heart development.

What Are the Main Symptoms of Ventricular Septal Defect?

The symptoms of a ventricular septal defect vary depending on the size of the defect and heart function. Small defects may be asymptomatic, but larger ones can present with the following signs:

Heart murmurs: A characteristic heart murmur can be heard during auscultation.

Difficulty breathing: Your pet may become short of breath easily after walks or even while resting.

Growth retardation: Weight gain may be slower than normal, or activity levels may decrease.

Fatigue: Your pet may spend the day sitting in one place or show little interest in play.

Coughing: Coughing may occur when blood accumulates in the lungs.

If you notice any of these symptoms, consult your veterinarian immediately.

A puppy experiencing difficulty breathing due to a ventricular septal defect

Signs Requiring Immediate Veterinary Attention

If your dog suddenly starts breathing rapidly, develops a bluish tint to its mouth, or collapses, these are signs that heart failure has progressed. This is a life-threatening emergency, so you should seek immediate care at an emergency veterinary hospital.

Symptoms and Management by Severity of Ventricular Septal Defect

Item	Mild	Moderate	Severe
Defect size	Small, restrictive defect (much smaller than the aortic annulus)	Medium-sized defect	Large defect comparable to the aortic annulus
Main symptoms	Only a heart murmur is heard, no symptoms	Shortness of breath after walks, fatigue	Shortness of breath even at rest, coughing, cyanosis/syncope
Treatment necessity	Manageable with regular observation alone	Consider medication if signs of left heart failure appear	Consider medication and surgical correction

Defect size is usually assessed by comparison with the aortic annulus diameter, and since there are individual differences, accurate assessment relies on the veterinarian's cardiac ultrasound diagnosis.

How Is an Accurate Diagnosis Made?

Ventricular septal defects are diagnosed when a veterinarian detects abnormal heart sounds during auscultation and confirms the condition with an echocardiogram. This ultrasound-based test provides real-time visualization of cardiac structure and blood flow, allowing precise assessment of the defect’s location and size, as well as overall heart function. Electrocardiograms and chest X-rays may also be performed if needed. Since diagnosis requires specialized equipment and expertise, it is safer for pet owners to visit a veterinary clinic rather than attempt to assess the condition themselves.

A veterinarian performing an echocardiogram on a puppy

What Are the Treatment Options?

Treatment depends on the size of the defect and the severity of symptoms. Small defects with limited blood flow can often be managed with regular monitoring if there are no significant symptoms. If a hemodynamically significant left-to-right shunt causes signs of left-sided heart failure, medications are used to reduce cardiac workload and alleviate symptoms. In cases of right-to-left shunting leading to cyanosis or polycythemia, sildenafil, which targets pulmonary hypertension, may be beneficial. Larger defects may require surgical correction; because pre- and post-operative care is critical, it is essential to consult with a veterinarian at a specialized clinic.

Daily Care Tips

Puppies with ventricular septal defects should avoid strenuous exercise and maintain a routine of regular meals and rest. Keep their activity level within the range recommended by your veterinarian, and provide a calm, stable environment to minimize stress. Avoid high-intensity play that puts extra strain on the heart, such as running or jumping, and keep walks short and slow. Monitor their heart condition through regular check-ups, and always administer medications exactly as directed by your veterinarian.

Stable daily care for a puppy with a ventricular septal defect

Breeds and Situations to Watch For

Certain breeds, such as the Keeshond, have a reported genetic predisposition, and large-breed dogs are also known to be predisposed. While breed-specific incidence trends have not yet been firmly established, if a genetic predisposition is suspected, breeding decisions should be made cautiously to avoid passing the condition to offspring. Additionally, in cases of significant septal defects, the risk of cardiac strain and complications is high; therefore, consult your veterinarian in advance before administering vaccinations or performing procedures requiring anesthesia, and regularly monitor heart health.

Reviewed by a veterinarian

Dr. Tony — Punnawat Phongkittirak

Veterinarian

A veterinarian who majored in veterinary medicine at Khon Kaen University, Thailand, and completed the IVSA program at North Carolina State University in the United States. Drawing on clinical experience at animal hospitals, he works in the pet healthcare field and is dedicated to building a digital care environment that connects pet parents with veterinarians.

Frequently Asked Questions

Is ventricular septal defect hereditary?

It is known to have a genetic predisposition. For example, studies have shown that in Cocker Spaniels, patent ductus arteriosus is associated with a defect in a single gene locus, and predisposition has also been reported in large-breed dogs. However, the genetic tendencies in specific breeds have not yet been firmly established, so it is advisable to consult with a veterinarian about genetic risks when breeding.

Can small defects heal on their own?

If the defect is small and blood flow is limited, the condition may progress favorably without placing a significant burden on the heart. However, whether it closes naturally varies from individual to individual, so regular cardiac ultrasound examinations are necessary to monitor the condition, and you should consult your veterinarian immediately if any symptoms arise.

How long does recovery take after surgery?

The recovery period varies depending on the size of the defect, the surgical technique used, and the puppy’s overall health. Rather than specifying a fixed timeline, it’s important to limit activity during this time, monitor progress through regular veterinary check-ups, and follow your veterinarian’s instructions.

What are the available medication treatments?

Medications to reduce the workload on the heart are used depending on the symptoms. In cases where a right-to-left shunt is accompanied by pulmonary hypertension and cyanosis, sildenafil, which targets pulmonary hypertension, may be helpful. Since medications are prescribed by a veterinarian based on the pet's weight and condition, do not administer or discontinue them without professional guidance.

Can dogs with a ventricular septal defect go for walks throughout their lives?

Physical activity is possible within the range recommended by your veterinarian. Avoid excessive exercise; short, slow walks are safer. If symptoms worsen, even walks may need to be restricted.

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References

[1] Textbook of Cardiovascular Medicine in Dogs and Cats, 2020, Chapter 7: Congenital Heart Diseases

[2] Small Animal Critical Care Medicine, 3rd Ed, 2021, Section on Congenital Cardiac Defects

[3] American College of Veterinary Internal Medicine (ACVIM) Consensus Statement on Congenital Heart Disease in Dogs, 2019