Heart Disease in Dogs: Symptoms, Causes, and Treatment

Heart disease in dogs is any condition that affects the heart’s ability to pump blood effectively, including valve disease, heart muscle disorders, arrhythmias, and heartworm infection.

Dogs in the early stages of heart disease don’t show outward signs. As the disease progresses, dogs can develop concerning symptoms, such as coughing, fatigue, or breathing difficulties.

Prompt diagnosis and ongoing management with medication, such as VETMEDIN^® (pimobendan), diet changes, or, in some cases, surgery can significantly improve a dog’s quality of life.

What Causes Heart Disease in Dogs?

There are various causes and risk factors for heart disease in dogs, which include the following: 

• Age-related changes 

• Poor nutrition, such as taurine deficiency 

• Heartworm infection 

• Congenital defects, such as patent ductus arteriosus  

• Chronic high blood pressure 

• Infections, such as parvovirus  

• Heart tumors 

• Severe periodontal disease (as bacteria from the mouth travels to the heart valves) 

Size is an important risk factor for heart disease in dogs. Smaller dogs (typically under 40 pounds), such as Cavalier King Charles Spaniels and Dachshunds, are predisposed to developing mitral valve disease. Larger dogs (typically over 60 pounds), including Boxers and Doberman Pinschers, have an increased risk for dilated cardiomyopathy.

Most Common Types of Heart Disease in Dogs

Let’s look at the most common types of heart disease in dogs: 

• Heart valve disease: The heart has four valves that keep blood moving in the right direction. When a dog is born with a faulty valve or a valve becomes diseased or damaged, blood flows backward in the wrong direction, creating turbulence. This causes a heart murmur and heart enlargement and can eventually lead to congestive heart failure as blood flow becomes less efficient. Myxomatous mitral valve degeneration (MMVD) is the most common type of heart disease in dogs, and tends to affect older, small-breed dogs. 

• Myocardial (heart muscle) disease: The heart is made mostly of muscle. If that muscle thins and weakens, the heart becomes less able to pump blood. This is called dilated cardiomyopathy, or DCM. Hypertrophic cardiomyopathy, or HCM, is another type of heart disease that develops when the heart muscle becomes too thick, preventing normal amounts of blood from filling the heart chamber. 

• Heartworm disease: Heartworms are spread through the bites of infected mosquitos. Adult heartworms live in the lungs’ larger blood vessels and in a dog’s heart. They cause a lot of inflammation and damage and can block the flow of blood from the heart into the lungs. 

• Arrhythmias: A heart rhythm that is too slow, too fast, or irregular can make it hard for the heart to pump blood to the lungs and rest of the body. 

• Shunts: Shunts are abnormal vessels or holes in and around the heart that prevent blood from circulating normally. Most cardiac shunts in dogs—such as patent ductus arteriosus and ventricular septal defect—are congenital (present at birth). 

• Stenosis: Puppies can be born with a narrowed area around their heart valves, making it hard for blood to pass through. Pulmonic stenosis and subaortic stenosis are the most common forms in dogs. 

• Pericardial disease: The pericardium is the sac that surrounds the heart. The heart can’t beat effectively if the pericardium becomes stiff or if the area between the pericardium and the heart fills with fluid (usually blood) or air. 

• Congestive heart failure, or CHF: A consequence of many types of heart disease, congestive heart failure develops when the heart can no longer pump blood well enough to meet the needs of the body. Fluid may leak out of blood vessels and collect in or around the lungs, in the abdomen, or within other tissues. 

Symptoms of Heart Disease in Dogs

Heart disease can occur slowly and may only cause subtle changes or sometimes, none at all initially. As the disease progresses, symptoms become more obvious to pet parents.

 Common symptoms of heart disease in dogs include: 

• Coughing (caused by fluid accumulation in the lungs or airway compression)

• Difficulty breathing 

• Becoming tired easily 

• Weakness 

• Weight loss 

• Diarrhea 

• Blue-tinged or gray gums (cyanosis) 

• Abnormal swellings (such as of the legs or belly) 

• Difficulty sleeping 

• Fainting 

• Collapse 

These signs can also be caused by other types of health problems, such as diseases affecting the lungs, so it’s important to get your dog to the veterinarian for an accurate diagnosis immediately.  

Stages of Heart Disease in Dogs

There are five stages of heart disease in dogs, which include the following

• Stage A: No clinical signs are present, but a dog has risk factors that predispose them to heart disease, such as their age, weight, or breed. This is where early screening by a veterinarian for at-risk dogs is crucial.
• Stage B1: This is the first stage where a dog develops a mild heart murmur that can be detected and monitored by a veterinarian. However, no outward signs of heart disease are present.
• Stage B2: While a murmur is present and a dog’s heart is becoming enlarged, there are still no symptoms present. VETMEDIN is the only FDA-approved medication to delay congestive heart failure in dogs in this stage.
• Stage C: A dog has progressed to congestive heart failure with corresponding symptoms, such as breathing changes, fluid retention, and exercise intolerance.
• Stage D: This is advanced heart disease where a dog has congestive heart failure that does not respond to standard therapy any longer.

How Veterinarians Diagnose Heart Disease in Dogs

Early diagnosis of canine heart disease improves patient outcomes and quality of life. With early diagnosis and treatment, veterinarians can detect changes in the heart and intervene to delay progression of the disease.

The first step in diagnosing heart disease in dogs is a complete physical examination. Be prepared to answer questions about your dog’s health history and the symptoms you have been seeing at home.  

A veterinary cardiologist may also be consulted. 

Diagnostic testing for heart disease is usually needed. This may include: 

• Chest X-rays to look at the heart’s shape and size and to evaluate the lungs and other structures in the chest 

• Electrocardiogram (ECG) to identify heart rhythm abnormalities 

• Echocardiogram (an ultrasound exam) to watch how blood flows through the heart and to evaluate heart valve and muscle function 

• Heartworm tests 

• Blood pressure measurement 

• Blood work 

Treatment of Heart Disease in Dogs

Heart disease in dogs is treated based on the underlying cause and severity. Treatment may include medications, surgery, and lifestyle changes to improve heart function and quality of life.

Medications for Heart Disease in Dogs

Medications are the most common treatment for heart disease in dogs and can:

• Help the heart to pump more efficiently. For example, VETMEDIN (pimobendan) improves the strength and function of heart muscle for dogs with preclinical and clinical signs of heart failure. It also dilates blood vessels, reducing the load on the heart. Available in both chewable tablet and oral solution form, VETMEDIN is typically given twice a day with or without food. 

Surgery and Procedures

Sometimes heart disease can be cured, and a dog’s symptoms may disappear. For example: 

• Adult heartworms can be eliminated with injections of melarsomine, a derivative of arsenic. 

• Some types of arrhythmias can be managed with a pacemaker or with surgical interventions. 

• Surgery may also be an option to correct a cardiac shunt, stenosis, or some types of valvular or pericardial disease. 

Diet and Lifestyle Changes for Dogs With Heart Disease

Your veterinarian may recommend modifying your dog’s diet and lifestyle changes to help support your dog’s heart health, including:

• Feeding a therapeutic diet: These diets are formulated to support heart function.
• Reducing sodium intake: Low-salt diets may help reduce fluid retention in dogs with congestive heart failure.
• Switching from boutique diets: Many dogs who developed dilated cardiomyopathy while eating a boutique diet have improved after switching to more traditional dog foods.
• Managing their weight: Weight loss may be recommended for dogs who are overweight to reduce the load on the heart.
• Adding supplements when appropriate: Nutritional supplements (taurine, for example) may benefit some dogs, depending on the underlying condition.

Prognosis of Heart Disease in Dogs

The prognosis for heart disease in dogs depends on how early it’s diagnosed and how it’s managed.

When heart disease in dogs is caught early and treated appropriately, dogs often live happily for many more years. In dogs without symptoms, studies have shown that VETMEDIN delays early signs of congestive heart failure and gives your dog more symptom-free days.

However, severe cases of heart disease or those that have progressed to congestive heart failure bring with them a more guarded prognosis.  

There usually comes a time when available treatment options can no longer maintain a dog’s quality of life, and humane euthanasia may be recommended.  

How To Prevent Heart Disease in Dogs

To prevent, or mitigate, heart disease in dogs, pet parents can take the following steps: 

• Ensure your dog receives regular wellness exams and blood work. 
• Discuss early screening options with your vet before clinical signs appear, especially for dogs with increased risk factors due to weight, age, or breed. By having conversations early, both you and your vet can be better informed in your pet’s care.

• Keep your dog up to date on routine vaccinations. 

• Feed your dog a high-quality, commercially available diet and maintain an optimal weight. 

• Ensure your dog stays up to date on heartworm prevention. 

• Brush your dog’s teeth and do professional dental cleanings to promote oral hygiene.