Heart Disease in Dogs

Heart disease in dogs can be present at birth or develop later in life. The most common acquired form is myxomatous mitral valve disease, a degenerative change of the heart valves that is especially common in small and toy breeds. Other important causes include dilated cardiomyopathy (a weakening and enlargement of the heart muscle), arrhythmias, heartworm disease, infections such as endocarditis, and congenital defects like patent ductus arteriosus or aortic stenosis. Some dogs are predisposed by breed, age, body size, or genetics, and heart disease may progress from a silent stage to congestive heart failure over time.

Risk factors and predispositions include: • Older age, especially in small-breed dogs with degenerative valve disease • Small and toy breeds, including Cavalier King Charles Spaniels, which are strongly predisposed to mitral valve disease • Large and giant breeds, and certain lines such as Doberman Pinschers and Boxers, with higher risk for dilated cardiomyopathy or arrhythmic disease • Congenital heart defects detected in puppies or young dogs • Heartworm exposure in areas where prevention lapses occur • Possible diet-associated dilated cardiomyopathy in some dogs

Diagnosis starts with a physical exam, listening for a murmur, gallop rhythm, irregular heartbeat, lung sounds, pulse quality, and signs of fluid retention. Your veterinarian will review breathing changes, coughing, stamina, appetite, fainting episodes, and any breed-related risk.

Common tests may include: • Chest X-rays to evaluate heart size and check for fluid in the lungs • Echocardiogram (cardiac ultrasound), the key test for evaluating valve disease, chamber size, pumping function, and many congenital defects • Electrocardiogram (ECG) to detect arrhythmias • Blood pressure measurement • Blood and urine tests to look for concurrent disease and to help monitor treatment safety • Heartworm testing when appropriate • Cardiac biomarkers or Holter monitoring in selected cases

At the appointment, some dogs can be diagnosed and staged the same day, while others need referral to a veterinary cardiologist for advanced imaging or rhythm monitoring.

Treatment depends on the type of heart disease, whether your dog has symptoms, and whether congestive heart failure is present. Many dogs need long-term monitoring even before symptoms appear. Common goals are to improve heart function, control fluid buildup, manage arrhythmias, and maintain quality of life.

Treatment may include: • Prescription heart medications such as inodilators, diuretics, ACE inhibitors, or antiarrhythmic drugs when indicated by your veterinarian • Pimobendan for selected dogs with myxomatous mitral valve disease, including ACVIM Stage B2 and many dogs with congestive heart failure • Oxygen therapy and hospitalization for dogs in active heart failure or respiratory distress • Restricted exercise during unstable periods, then moderate activity as advised by your vet • Weight management, routine rechecks, bloodwork, and repeat chest X-rays or echocardiograms • Heartworm treatment when heartworm disease is the cause, using a veterinarian-directed plan • Interventional or surgical correction for certain congenital defects, such as patent ductus arteriosus, in appropriate candidates

Never start, stop, or adjust heart medications without veterinary guidance. If your dog's breathing worsens, call your vet right away.