Overview of the Heart

The heart is an essential organ involved in the cardiovascular system. The structure and function of the heart in dogs and cats are the same as those in humans. The heart is composed of four chambers and four valves. The muscle of the heart is responsible for pumping blood, the valves ensure blood flows in the right direction, and the electrical conduction results in contraction of the heart. Any changes to the structure and function of the heart will result in blood being pumped ineffectively.

Common Heart Diseases in Dogs

Myxomatous mitral valve disease (MMVD) is the most common heart disease in dogs; 70% of dogs with heart disease are diagnosed with MMVD. The mitral valve separates the left atrium from the left ventricle. It ensures blood that moves from the left atrium to the left ventricle remains in the ventricle after the valve closes. Over time, it becomes weak and soft, resulting in the blood flowing backwards from the left ventricle to the left atrium (improper direction of blood flow). Cavalier King Charles Spaniels have a genetic predisposition to MMVD, but this can occur in all dogs (small > large breed), with the exact cause being unknown.

Dilated cardiomyopathy (DCM) is another common acquired heart disease in dogs. This is when there is an abnormality in the heart muscle. The chambers of the heart become dilated and weak, causing the heart muscles to pump blood ineffectively. One of the causes is diet-related. Many of the grain-free diets contain high quantities of peas, chickpeas, lentils, and other dry beans, which are associated with causing DCM. It is unclear the exact mechanism, but it is recommended to avoid grain-free diets, if possible, to reduce the risk of DCM. Some breeds are predisposed to DCM, such as Dobermans, Boxers, and Irish Wolfhounds, due to a genetic component.

Common Heart Disease in Cats

Hypertrophic cardiomyopathy (HCM) is the most common heart disease in cats. In this disease, the left ventricle increases in muscle wall thickness, making the chamber smaller. As a result, there is decreased filling of the left ventricle and then a decrease in blood pumped out of the heart to the body. The exact cause of the disease is still poorly understood. Any cat can develop HCM, but Maine Coons, Ragdolls, and Sphinx cats have a genetic predisposition.

Signs of Heart Disease

Clinical signs of heart disease in dogs and cats are very similar. The common signs are as follows:

• Difficulty breathing

• Coughing (dogs > cats)

• Exercise intolerance

• Weight loss

• Lethargy, weakness and/or collapse

• Enlarged/bloated abdomen

Diagnosis, Treatment, and Monitoring

The first step in diagnosing heart disease is a physical exam. A veterinarian will listen to the heart during each exam and can detect a heart murmur if one is present. Based on the degree of the murmur and clinical signs present, a full cardiac workup may be recommended. This includes the following:

• Radiographs: determine the overall size of the heart and assess the lungs

• ECG: recording of the electrical conduction of the heart and determine the rhythm

• Echocardiography: ultrasound exam of the chambers and valves of the heart

Prognosis is dependent on the type of heart disease and the stage at which it is diagnosed. Initial treatment often includes medications to support the heart function and treat arrhythmias. Although medication does not cure heart disease, it does slow the progression. It is important to administer the medication as directed by your veterinarian. Monitoring the progression includes frequent rechecks and diagnostics. It also includes monitoring your pet at home for new or worsening signs listed above.

Although adult-onset heart disease does not have a cure at this time, with proper management and monitoring, your pet can have a good quality of life until it has reached the end stage.

References

(N.d.) Merck Veterinary Manual. Retrieved March 10, 2026, from https://www.merckvetmanual.com/

ABCDs of Myxomatous Mitral Valve Disease. (2021). Cardiac Education Group. Retrieved March 10, 2026, from https://cardiaceducationgroup.org/

ABCDs of Feline Cardiomyopathy. (2021). Cardiac Education Group. Retrieved March 11, 2026, from https://cardiaceducationgroup.org/

Keene, B. W., Atkins, C. E., Bonagura, J. D., Fox, P. R., Häggström, J., Fuentes, V. L., … Uechi, M. (2019). ACVIM consensus guidelines for the diagnosis and treatment of myxomatous mitral valve disease in dogs. Journal of Veterinary Internal Medicine, 33(3), 1127–1140. doi:10.1111/jvim.15488

Medicine, C. for V. (n.d.). FDA investigates potential link between Diet & Heart Disease In Dogs. U.S. Food and Drug Administration. FDA. Retrieved March 10, 2026, from https://www.fda.gov/animal-veterinary/outbreaks-and-advisories/fda-investigation-potential-link-between-certain-diets-and-canine-dilated-cardiomyopathy