Heart Disease in Dogs

Heart disease in dogs is a broad term, not one single diagnosis. It includes acquired problems that develop over time, such as myxomatous mitral valve disease in small and older dogs, and dilated cardiomyopathy in some larger breeds. It also includes congenital defects present from birth, rhythm problems, and heartworm-related disease that affects the heart and blood vessels leading to the lungs. Many dogs do not look sick early in the course of disease, which is why a murmur or abnormal rhythm found during a routine exam can matter so much.

The heart’s job is to move blood forward efficiently. When a valve leaks, the heart muscle weakens, or blood flow is obstructed, the body has to compensate. Over time, that strain can lead to enlargement of the heart, fluid buildup in the lungs or belly, poor exercise tolerance, fainting episodes, or congestive heart failure. Left-sided heart failure often causes coughing and breathing trouble from fluid in the lungs, while right-sided failure is more likely to cause abdominal fluid buildup.

Not every murmur means advanced disease, and not every dog with heart disease needs the same treatment. Some dogs need only monitoring for a period of time. Others benefit from medications before they ever show symptoms, while some need emergency stabilization or referral to a veterinary cardiologist. The most helpful next step is getting the exact diagnosis and stage from your vet, because treatment choices depend on the specific heart problem rather than the word heart disease alone.

Diagnosis starts with a careful history and physical exam. Your vet will listen for a murmur, gallop rhythm, crackles in the lungs, or an irregular heartbeat. They may ask about cough, fainting, sleep breathing rate, appetite, and exercise tolerance. A murmur tells your vet that blood flow is turbulent, but it does not identify the exact disease by itself. Some dogs with serious rhythm problems may not have a loud murmur at all.

Common first-line tests include chest X-rays, blood pressure, ECG, and bloodwork to check kidney values, electrolytes, and overall health before medications are started or adjusted. Chest X-rays help show heart size and whether fluid is present in the lungs. An ECG helps identify arrhythmias. In some cases, your vet may recommend NT-proBNP or other cardiac biomarkers to help distinguish heart-related breathing signs from other causes.

An echocardiogram is often the most useful test for defining the exact heart problem. This ultrasound shows valve leakage, chamber enlargement, pumping strength, congenital defects, and some forms of pulmonary hypertension. It is especially important when treatment decisions depend on staging, such as deciding whether a dog with mitral valve disease has reached the point where preclinical medication may help. Dogs with suspected complex disease, fainting, severe arrhythmias, or congenital defects are often referred to a cardiologist for advanced imaging and treatment planning.

Heart disease in dogs can be congenital or acquired. Congenital disease means a dog is born with the defect. Common examples include patent ductus arteriosus, pulmonic stenosis, subaortic stenosis, and ventricular septal defect. These problems are often found in puppies or young dogs, sometimes after your vet hears a murmur during a wellness exam. Some congenital problems stay mild, while others can lead to heart enlargement, poor growth, or heart failure if not treated.

Acquired heart disease develops later in life. The most common acquired problem in dogs is degenerative mitral valve disease, especially in small and older dogs. Dilated cardiomyopathy is another major cause and is seen more often in large and giant breeds such as Dobermans, Great Danes, and Boxers, though other breeds can be affected. Arrhythmogenic cardiomyopathy, pericardial disease, and heartworm disease can also affect heart function and circulation.

Risk factors depend on the condition. Breed, age, body size, genetics, and sex all matter for some diseases. Heartworm exposure matters in endemic areas if prevention is inconsistent. Some cases of DCM have been linked to nutritional issues, including taurine deficiency in certain situations, and diet-associated DCM remains an area of ongoing study. Because causes vary so much, your vet may recommend different tests for a Chihuahua with a new murmur than for a Doberman with fainting spells.

Not all heart disease can be prevented, especially inherited or age-related conditions. Still, early detection makes a real difference. Routine exams help your vet find murmurs, rhythm changes, or subtle breathing changes before your dog looks obviously ill. For breeds at higher risk of inherited heart disease, screening with your vet or a cardiologist may be recommended even before symptoms appear.

Year-round heartworm prevention is one of the clearest ways to reduce a serious and potentially fatal cause of heart and lung disease. Prevention matters even when mosquitoes seem seasonal, because missed doses and travel can increase risk. If your dog is on prevention, keep testing and refill timing on schedule based on your vet’s advice.

General wellness also supports heart health. Keep your dog at a healthy body condition, stay current with dental care, and avoid changing to unusual diets without discussing them with your vet, especially in breeds at risk for DCM. If your dog already has a murmur or diagnosed heart disease, prevention shifts toward slowing progression: regular rechecks, medication monitoring, and watching resting breathing rate at home can help catch changes early.

Prognosis depends on the exact diagnosis, how advanced the disease is, whether congestive heart failure is present, and how well the dog responds to treatment. Some dogs with mild valve disease live comfortably for years before needing medication. Others, especially dogs with advanced DCM, severe arrhythmias, or certain cancers affecting the heart, may have a more guarded outlook. Congenital defects vary widely too. Some can be corrected or improved with procedures, while others require lifelong monitoring.

Recovery is usually less about curing the disease and more about stabilizing the dog, controlling symptoms, and preserving quality of life. Dogs in heart failure often improve noticeably once fluid is reduced and medications are adjusted. That said, heart disease is usually a chronic condition. Rechecks matter because medication doses, kidney values, electrolytes, and breathing status can change over time.

At home, pet parents often help most by giving medications consistently, tracking resting respiratory rate, noting appetite and stamina, and contacting your vet early if cough, breathing effort, or fainting worsens. Ask your vet what changes count as urgent for your dog’s specific diagnosis. Many dogs do well for meaningful periods with a realistic plan that matches the stage of disease and the family’s goals.