Heart Disease

How the heart works:

The heart can be regarded as a large pump. It pumps blood which carries oxygen and nutrients throughout the circulatory system to all parts of the body. The heart is largely composed of a muscle called the myocardium. It is divided into four chambers. Two upper chambers ‘the atria’ which receive blood returning to the heart from the veins and two lower chambers  ‘the ventricles’  which contract and eject blood into the arteries and throughout the circulatory system. The heart also has valves at opening of the atria and between the atria and ventricles. It is divided into a right and left side by  a tough wall or septum. The right side of the heart pumps blood to the lungs where the blood is oxygenated. This blood then returns to the left side of the heart from where the oxygenated blood is pumped throughout body. The left side of the heart is larger since it has a greater workload.

Types of heart disease:

Congenital heart disease

This is by far the less common type of heart disease accounting for only 5% of cases. It can be due to failure of the walls separating the heart to form properly (hole in the heart), faulty valves, or wrongly positioned or narrowed blood vessels. Often these problems are only identified once the young animal becomes mobile and is seen to be slower or weaker than its litter mates. Sometimes surgery can be used to correct these defects.

Acquired heart disease

This accounts for 95% of cases seen. The two main types of acquired heart disease seen are chronic acquired degenerative valvular disease and dilated cardiomyopathy.

Valvular Disease

This is a gradual degeneration of the heart valves which results in blood leaking through the valves when they are shut.The heart then becomes an ineffective pump. Small breeds of dog are more commonly affected and the disease is seen in middle aged to old dogs. The cause is unknown.

Dilated Cardiomyopathy

In this condition the heart dilates and as it does so the muscle wall becomes thinner and weaker. It affects mainly large breeds and is seen in young and middle aged dogs. Males are more often affected than females. Like valvular heart disease the cause is unknown.

Signs of heart disease:

The signs of heart disease are varied but all or some of the following may be noticed: coughing, difficulty breathing, swollen abdomen, exercise intolerance, weight loss, inappetance, collapse or depression.

Confirmation of heart disease:

Though the development of some or all of the above signs may make your veterinary surgeon suspicious of heart disease, specific tests may be required to make an accurate diagnosis and allow for logical treatment. Some of the tests are described below:

Stethoscope – listening to the heart with a stethoscope yields much valuable information. Heart murmurs can be detected in this way.

Ultrasound – can give valuable information as regards the heart chamber size, condition of the valves and contractility of the heart

X-ray – commonly X-rays of the chest and sometimes abdomen are taken in suspect cases of heart disease. Information gained from x-rays includes whether or not the heart is enlarged or if there is evidence of pulmonary congestion.

ECG – This records the electrical activity of the heart and detects any cardiac arrhythmias or irregularities in the heart’s rhythm

Blood tests – these will detect any underlying disease elsewhere in the body which may be affecting the heart or concurrent disease which may influence the choice of drug used in treating the heart disease. Some blood tests are becoming available that may directly help diagnose heart disease.


With few exceptions heart disease can not be cured but with modern treatments the condition can be successfully managed to improve your pet’s quality of life and to lengthen his or her lifespan. The choice of drug treatment depends on the exact cause of the condition. Pimobendin works by increasing the strength of the heart’s contraction while ACE-inhibitors dilate the blood vessels thus reducing the heart’s work load. Digoxin can be used to treat irregular rhythms. Frusemide reduces pulmonary congestion and hence alleviates such symptoms as coughing. Millophyline and aminophylline dilate the airways and in so doing may ease the cough. It is important to understand that your pet will be on treatment for life. Once stabilised on the correct course of treatment repeat prescriptions can be given but regular check-ups are required, usually every three months. This is essential to monitor the course of the condition and where necessary to alter treatment regimes . It is also a requirement by law.