Congenital Heart Disease

The severity of signs depends on the specific defect and how significantly it disrupts normal blood flow. Many pets with mild defects are asymptomatic except for the murmur; others show obvious signs from a young age:

• Heart murmur detected at the first puppy or kitten exam — often the sole finding in mild defects
• Exercise intolerance — a young pet that cannot keep up with littermates or tires unusually quickly
• Failure to thrive — poor weight gain or stunted growth compared to siblings
• Labored breathing or rapid respiratory rate
• Coughing, which may indicate fluid beginning to accumulate in the lungs
• Fainting or collapse (syncope), particularly during play or excitement
• A continuous machinery-like murmur heard over the left chest — nearly diagnostic of patent ductus arteriosus (PDA)

Some pets with significant defects remain compensated for months to years before signs of heart failure emerge. Others deteriorate rapidly. The trajectory is impossible to predict without imaging.

Congenital defects arise from abnormal fetal cardiac development and are often heritable. The most clinically important defects in dogs and cats include:

• Patent ductus arteriosus (PDA) — the most common congenital cardiac defect in dogs. The ductus arteriosus is a fetal blood vessel that should close at birth; when it remains open, blood is continuously shunted from the aorta into the pulmonary artery, volume-overloading the left heart. Miniature and Toy Poodles, Bichon Frises, Maltese, and German Shepherds are commonly affected. PDA is also occasionally seen in cats. Left untreated, most dogs with PDA develop congestive heart failure — but surgical ligation is curative when performed before irreversible heart damage occurs.
• Pulmonic stenosis (PS) — narrowing of the pulmonic valve (the valve between the right ventricle and the pulmonary artery), forcing the right ventricle to pump against increased resistance. Bulldogs, Boxers, Mastiffs, and Samoyeds are predisposed. Mild PS requires no treatment; severe PS may be managed with balloon valvuloplasty (a catheter-based procedure to widen the valve).
• Subaortic stenosis (SAS) — a fibrous ring just below the aortic valve that obstructs left ventricular outflow; the most common congenital defect in large dogs. Golden Retrievers, Newfoundlands, Rottweilers, and Boxers are highly predisposed. SAS carries a risk of sudden death in severe cases; management is primarily medical.
• Ventricular septal defect (VSD) — a hole in the wall between the left and right ventricles; small VSDs are often well tolerated for life, while large ones cause significant volume overload and eventually heart failure. VSDs are more common in cats than the other defects listed here.

A thorough cardiac evaluation for a young pet with a murmur begins with characterizing the murmur itself and proceeds to imaging:

• Auscultation — the location, timing, quality (harsh, blowing, machinery-like), and intensity of the murmur give important clues. A continuous murmur over the left base is nearly pathognomonic (highly characteristic) for PDA; a systolic murmur at the left base suggests PS; a harsh systolic murmur radiating up the neck suggests SAS.
• Echocardiogram (cardiac ultrasound) — the definitive diagnostic tool. Dr. D'Urso's echocardiogram defines the specific defect, measures chamber dimensions and wall thickness, quantifies the pressure gradient across any obstruction, and documents whether there is already evidence of cardiac remodeling or dysfunction. This information is essential before any decision about intervention.
• Chest radiographs (X-rays) — assess overall heart size and the shape of the cardiac silhouette; can show characteristic changes (e.g., left-heart enlargement and a dilated aortic arch with PDA)
• Electrocardiogram (ECG) — identifies arrhythmias and provides additional evidence of chamber enlargement patterns
• Blood pressure measurement — baseline and for monitoring if medical management is initiated

The approach to treatment varies significantly by defect type and severity:

• PDA surgical ligation — the treatment of choice, and in most dogs it is curative. Dr. Schulman performs PDA ligation on-site at Dog & Cat Hospital Calabasas. Surgery is ideally performed before six months of age and before significant left-heart enlargement develops. Dogs that receive timely ligation typically have a normal life expectancy; those left untreated usually develop heart failure within one to two years.
• Balloon valvuloplasty for severe pulmonic stenosis — a catheter is passed through the jugular vein or femoral vein and a balloon is inflated across the narrowed valve to widen the opening. This is a referral procedure performed at a specialty or academic center; Dr. D'Urso helps determine which patients meet the criteria for intervention versus long-term medical monitoring.
• Medical management for SAS — atenolol (a beta-blocker) is used to reduce the heart rate and oxygen demand of the thickened left ventricle, but cannot remove the obstruction. Activity restriction is important in severely affected dogs. Routine Holter monitoring screens for arrhythmias, which are a major cause of sudden death in severe SAS.
• Observation for small VSDs — many small ventricular septal defects never cause clinical problems and are managed by periodic monitoring. Large VSDs causing heart enlargement may require medical support or, in some cases, interventional closure (referral).

Early detection is the most powerful factor in outcome. A puppy or kitten diagnosed with PDA and referred for surgery promptly has an excellent chance of a completely normal life.

Any puppy or kitten with a heart murmur at their first wellness exam — even if it sounds quiet or seems to bother no one — deserves an echocardiogram to identify its cause. Some of the most correctable defects (PDA in particular) produce signs that owners easily attribute to normal puppy playfulness, and the window for ideal surgical timing can pass quickly. Breeders with predisposed lines should have all breeding stock and litters screened. If you have adopted or purchased a young dog or cat and were told it has a murmur, or if your pet seems to tire too quickly for its age, our team can provide a complete cardiac evaluation in one visit. Dr. D'Urso and Dr. Schulman collaborate directly here, so evaluation, diagnosis, and surgical planning can happen without the delay of coordinating between multiple practices. Book an appointment today.