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Heart Disease in large dogs
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Dog Advice: heart disease in large dogs

Monitoring the signs

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Dilated Cardiomyopathy (DCM)

Dilated Cardiomyopathy (DCM) is a disease that affects the heart muscle. DCM most commonly affects medium to large breed dogs, such as Dobermans, Boxers, Irish Setters, German Shepherds, Great Danes, St Bernards and Irish Wolfhounds. 

DCM is characterised by two phases, a long and ‘silent’ preclinical phase where the dog will appear normal and healthy and then a shorter clinical phase, i.e. heart failure, when the dog appears ill or might suddenly die. The preclinical phase is important because, although your pet may look healthy, the changes of heart disease have already begun and this is the time to start treatment.

In DCM, the heart muscle gradually becomes weakened and floppy. The heart enlarges and stretches, and becomes very inefficient at pumping blood around the body. Because the heart’s ability to pump is impaired, circulation is also impaired. A dog with DCM can often live with the problem for a period of time as the body naturally makes adjustments to cope with the changes. However, at some point, the disease exceeds the body’s ability to cope, and the dog will become unwell and shows signs of heart failure.


How is DCM diagnosed by my vet?

When your vet checks over your dog, they may find signs relating to heart disease and/ or congestive heart failure. Listening to your dog’s heart with a stethoscope will allow a vet to pick up a murmur if it is present. The heart rate and rhythm can also be assessed using a stethoscope. Your vet may also detect harsh sounds when listening to the lungs. The vet may also pick up other signs that your dog’s heart is not working well, such as fluid in the abdomen and poor pulses. Regular veterinary visits are very important for early detection of heart disease or to monitor the treatment of a dog with heart disease. Your vet may recommend further tests to help determine the cause of these abnormalities.

These tests may include:

• Blood test: Blood tests may be recommended to check your dog’s health to see if they are suitable for medication and to check that the rest of their body is healthy. There are also specific heart-related markers in the blood which are often used to screen for DCM.

X-ray: X-rays are very useful to assess your dog’s heart and lungs. Commonly when a heart is having problems it will get larger and fluid may build up on the lungs. Both of these can be detected with x-rays.

• Echocardiogram: This is an ultrasound scan of the heart. It is one of the most accurate methods of diagnosing heart disease and can be used to assess the heart whilst in action. The heart’s walls, chambers, valves and blood vessels can be accurately observed.

• Electrocardiogram: Regular veterinary visits are very important for early detection of heart disease or to monitor the treatment of a dog with heart disease. Electrocardiograms (ECGs) can record the electrical activity of the heart and can be used to diagnose rhythm problems.

How to help your dog


Regular mild to moderate exercise is thought to be beneficial for dogs that have only mild signs of heart disease. However, if your dog seems tired, stop exercising and allow them to rest. It is very important to seek your vet’s advice about whether exercise is suitable for your dog and to what level. Contact your vet if your pet collapses or seems very weak during activity.


Yearly screening is usually recommended for dogs at risk. Depending on the results of the tests, your vet may suggest a treatment regimen or test again as needed. Your vet may suggest that you monitor certain aspects of your dog’s health to help gain a better understanding of how their heart is coping. There are two main ways in which you can monitor your dog’s heart condition at home: 1. Monitor your dog’s sleeping breathing rate. 2. Keep a diary of their activity levels, appetite and demeanour. Both of these methods of monitoring your dog’s health may help your vet understand how their condition is progressing. 

How do I recognise DCM in my dog?

Signs of heart failure can initially be quite mild and so may be difficult to pick up. However, as the disease progresses, the signs can become more severe as the heart’s function deteriorates. This stage is known as congestive heart failure, when the heart is no longer able to pump sufficient blood around the body. These signs occur because of fluid build-up or because the vital organs are not supplied with as much blood and oxygen as they require. In DCM, the disease tends to progress quite quickly and can even cause sudden death. 

Signs include: 

• Fainting 
• Weakness 
• Lack of energy / depression 
• Laboured breathing 
• Coughing 
• Poor appetite 
• Weight loss 
• Swollen abdomen (ascites)