The feline heart is a hard-working organ, and is divided anatomically into left and right sides. Valves allow for blood flow through the heart. The left atrium, the right atrium, the left ventricle, and the right ventricle comprise the four heart chambers. The external heart “sac” is designated the pericardium, and the myocardium is the actual muscle of the heart. The endocardium is the inner layer of cells in the heart. Heart disease, or cardiac disease, can affect any of these components.

“Dirty” blood (carrying carbon dioxide from organs, tissues, and cells) enters the right atrium through large vena cava veins and flows to the right ventricle via the tricuspid valve. It travels through the pulmonary artery (via the pulmonary valve) to the lungs to collect oxygen and eliminate carbon dioxide and re-enters the left atrium through the pulmonary vein. The mitral valve ferries the oxygen-rich blood to the left ventricle, and the aorta (entering through the aortic valve) carries “clean” oxygen-rich blood to the remainder of the body.

Heart disease, or cardiac disease, can be a devastating clinical condition in companion animals. Early recognition and treatment can facilitate appropriate clinical management and a long life.

Types of Heart Disease in Cats

Cardiac disease is classified as either congenital or acquired.

Most congenital cardiac defects are present from birth or near birth, and include conditions such as septal defects (atrial and ventricular), valve dysplasias, and congenital cardiomyopathies. All involve some degree of structural heart component or valvular dysfunction. Although some breed-associated congenital conditions are detected early in life, others are not identified until adulthood; Maine Coon cats are frequently diagnosed with cardiac disease.

Acquired conditions can also affect any heart component and are not present at or near birth. They develop over time and with age, and many are not pathologic or progressive. However, some may be associated with progressive heart and valve disease.

• The most common acquired feline heart disease is hypertrophic cardiomyopathy; this is a thickening of the heart muscle which causes heart failure.
• Endocarditis, myocarditis, and pericarditis are structural inflammatory conditions that result from a variety of causes, including infectious, traumatic, and immune conditions.
• Pericardial effusion occurs when excessive fluid collects between the layers of the pericardial sac; causes are diverse and can include cancer.
• Valvular endocardiosis, valvular degeneration, and valvular regurgitation/insufficiency are frequently-identified valvular conditions.
• Hyperthyroidism can also affect the feline heart.

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