Heart disease is one of the most commonly diagnosed diseases of dogs in the United States and Europe. ¹ In dogs, heart disease can be either congenital or acquired. Common congenital heart conditions include aortic stenosis (AS), patent ductus arteriosis (PDA), ventricular septal defect (VSD), and pulmonic stenosis (PS). Some of these conditions appear to have a hereditary component and are found more frequently in certain breeds or lines of purebred dogs. Acquired heart disease is more common than congenital disease in dogs and cats. However, companion animals rarely suffer from atherosclerosis and coronary disease. ² The most common form of acquired heart disease in dogs is chronic valvular disease. There are many different types of valvular diseases; chronic mitral insufficiency, tricuspid insufficiency, mitral stenosis, aortic insufficiency, pulmonic insufficiency, and bacterial endocarditis are the most common forms that are diagnosed in dogs. Of these, chronic mitral insufficiency is the most common and is typically observed in middle- to older-age dogs. It also appears more often in certain breeds such as the Cavalier King Charles Spaniel, Dachshund, Miniature and Toy Poodles, Chihuahuas, and many of the Terrier breeds. ³ In chronic mitral insufficiency, there is retrograde flow of blood from the left ventricle to the left atrium during ventricular systole or contraction. This results in reduced flow to the peripheral circulation, an increased backflow to the atrium, and blood volume overload in the heart. Dogs with this heart problem usually eventually develop CHF.

Another common heart problem in dogs is dilated cardiomyopathy (DCM). This disease typically occurs in dogs that are middle-aged to older; however, some breeds have been reported to develop it early in life. For example, Portuguese Water Dogs can develop DCM and show clinical signs of CHF as young as 2 to 3 months of age. ⁴ There also appears to be a genetic predisposition in several large- and giant-breed dogs. Irish Wolfhounds, Great Danes, Saint Bernards, Newfoundlands, Doberman Pinschers, and Boxers are breeds that show an increased incidence of DCM. ^{5. and 6.} Over half of all Dobermans and one third of Boxers are estimated to develop the disease in their lifetime. ^{5. and 6.} Although they are not considered a large- or giant-breed dog, Cocker Spaniels also have a tendency to develop a form of DCM that previously was considered only a feline cause of cardiomyopathy; DCM in Cocker Spaniels can be caused by a taurine deficiency.

DCM is a primary myocardial disease characterized by cardiac chamber enlargement, arrhythmias, and diminished cardiac contractility. Eventually these dogs show signs of CHF, if not managed properly. Clinically, these dogs can show signs of weakness, collapse, lethargy, abdominal distention, tachycardia, tachypnea, dyspnea, coughing, syncopy, weight loss, anorexia, and sudden death. Two multibreed studies done on dogs with DCM demonstrated survival after 1 year of being diagnosed with DCM at only 17.5% and 37.5%, respectively, with the median survival times of only 27 and 65 days, respectively. ^{7. and 8.}

In cats, DCM used to be the most common type of heart disease. However, in the late 1980s Pion et al. ⁹ reported an association with DCM and taurine deficiency in cats. Fortunately, it was found that administration of taurine to cats’ diets could reverse the myocardial changes seen. ⁹ Since that finding was demonstrated, commercial cat food manufacturers have increased the amount of taurine in their products, and there has been a dramatic reduction in the incidence of feline DCM. Although it is possible to still see a case of DCM in cats fed a poor-quality homemade, vegetarian, or unbalanced diet, most cases of feline DCM are seen as a taurine-independent variant of DCM, or seen as end-stage hypertrophic cardiomyopathy (HCM). ¹⁰

Currently in cats, the most common heart disease is HCM. Its incidence appears to be increasing. A recent publication reported 21% of overtly healthy cats had heart murmurs, and 86% of these cats, when evaluated using echocardiography, had structural cardiac disease, primarily HCM. ¹¹ This is in comparison to studies conducted in the 1970s and 1980s where only 1.6% of all cats referred to a veterinary hospital were reported to have HCM. ¹² Although most cats listed to be at risk for this condition include domestic long- and short-haired cats, in purebred lines, Maine Coon cats seem to have a heritable or familial tendency toward the disease. ¹³

Cats with HCM have a symmetrical or asymmetrical hypertrophy of the left ventricular wall, papillary muscles, and septum restricting the size of the left ventricular lumen. The myocardial cells are enlarged, and the left ventricular filling is impaired from reduced left ventricular compliance. There often is a secondary left atrial enlargement present. If there is atrial enlargement, arrhythmias may be more commonly detected. Cat with HCM usually develop CHF and arterial thromboembolism (ATE) with ATE reportedly developing in up to 48% of affected cats. ^{12.14.15.16. and 17.} Clinically, cats with HCM demonstrated signs of weakness, labored breathing, lethargy, syncope, arrhythmias, and hindlimb pain or paralysis if ATE was present. Cats with HCM have a mean survival time of less than 2 years. ¹⁴

Cardiac cachexia is defined as muscle wasting and weight loss that commonly occurs in humans, dogs, and cats with cardiac disease. For example, one study reported that more than 50% of dogs with DCM showed some degree of cardiac cachexia. ¹⁸ Similar to cancer cachexia, the weight loss that occurs with cardiac cachexia includes a substantial and unusually high loss of lean body tissue. Although many veterinarians consider cachexia to be an end-stage development in animals with CHF, it can occur in early stages of CHF. ¹⁹ Similar to cancer cachexia, the metabolic changes may precede obvious physical changes. The loss of lean body mass can affect many different systems and is associated with shortened survival time. As muscle tissue is metabolized, the animal experiences muscle wasting, a loss of strength, and eventually compromised immune function. For example, dogs with cardiac cachexia have lower CD4+ lymphocytes and are at increased risk for anemia. ²⁰

Anorexia is a very common problem in pets with CHF and contributes to the onset of cardiac cachexia. It has been reported to occur in up to 84% of dogs with CHF and in at least 38% of cats with cardiac disease. ^{21.22. and 23.} Reduced appetite may be secondary due to the fatigue and respiratory dyspnea commonly seen with CHF, but it can also be due to side effects of medications or feeding a new food that may be less palatable. ²⁴ An increase in energy requirements is also a factor that needs to be evaluated when considering the loss of lean body mass. In humans, it has been documented that some may need up to a 30% increase in overall energy requirements when diagnosed with CHF. ²⁵ This increase in energy requirements may be due to tachycardia or tachypnea. ¹⁰ Therefore dogs and cats may also benefit from increasing the total energy in their diet. Metabolic alterations may also contribute to the loss of lean body mass. Cytokine elevation, tumor necrosis factor, and interleukin-1 occur in patients with CHF. ²⁴ These inflammatory mediators can increase energy requirements, increase breakdown of lean body mass, and directly cause anorexia. ²⁴ Interestingly, in 68% of dogs with CHF, anorexia was a contributing factor for owners opting to euthanize their pets. ²¹ Therefore controlling, or at least addressing, the issue of cardiac cachexia and anorexia nutritionally is important to prolong survival time in dogs and cats with CHF.

Medical treatment goals for cats with HCM are those that include reducing heart rate, management of CHF when present, and either treating or preventing ATE. Common medications to achieve this include diltiazem, beta-blockers, furosemide, and angiotensin-converting enzyme (ACE) inhibitors. To prevent or treat ATE, aspirin, warfarin, dalteparin or enoxaparin, and clopidigrel are common options. Dogs with DCM are often prescribed medications such as ACE inhibitors, beta-blockers, pimobendan, digoxin, antiarrhythmics, and diuretics such as furosemide.

In addition to medical therapy, nutritional modification is an important component of treatment protocols for dogs and cats with CHF. Nutritional modification can support a good quality of life, and, in some cases, may ameliorate some of the clinical effects of heart disease.

In many cases, preventing or reversing anorexia is part of nutritional treatment. Because some medications given to heart patients can cause anorexia as a side effect, reducing the dose or altering the number of doses per day may be helpful. Food palatability is an important consideration. Many therapeutic foods are available in both a canned and dry form, so switching between the two may be beneficial. Warming the food in a microwave (either canned foods or wetted dry foods) and offering small, frequent meals throughout the day can also help with acceptance. Additionally, adding small amounts of certain flavor enhancers such as honey, yogurt, or diluted tuna juice may improve acceptance of the food.