The old maxim 'A healthy pet is a happy pet' still holds true. Keeping your pet healthy is an important part of pet ownership. The heart is at the centre of health. However because it is so important the heart has a huge reserve capacity that means that animals can cope with quite severe impairment to heart function whilst showing few obvious signs of illness. Your partner in caring for your pet should be your vet. Regular visits to a vet for routine health checks and preventative health care such as vaccination allow you and your pet to build a relationship with your vet. Early detection of heart diseases will allow your vet to give more effective treatments.
Modern pets are living longer than their predecessors and as a result heart disease is becoming increasingly common in dogs and cats. Some animals are born with defects of the heart - these can cause problems in young animals but often do not cause signs until later in life. Many heart diseases develop as animals get older due to the effects of damage or ageing on the heart.
Your questions answered
How does the heart work?
The dog's heart, like that of humans, is a muscular pump with four separate chambers. The right side of the heart sends blood to the lungs where it picks up oxygen. The left side of the heart pumps the blood around the body. The four areas of the heart are separated by valves which ensure that blood always flows in the correct direction through the heart.
What causes heart disease?
Heart disease may affect any area of the heart:
The valves within the heart may fail to develop properly, eg mitral dysplasia, or may degenerate as a result of ageing (endocardiosis). Specific infections can affect the heart valves (endocarditis). Abnormal valves allow leakage of blood between heart chambers even when they are closed. When valves leak abnormal blood flow can be detected when listening to the heart (a murmur) and on ultrasound.
In general terms the heart muscle may be either too thick or too thin. If the muscle is too thin the heart is unable to contract properly and if the muscle is thick the heart cannot relax and therefore does not fill with blood between contractions. In either case the heart is unable to pump sufficient blood out.
Abnormal electrical conduction affects the rate and rhythm of the heart. Electrical abnormalities can be caused by disease outside the heart. If the heart beats too quickly there is not enough time for it to fill properly between beats and so it pumps less blood with each beat. If the heart beats too slowly there are not enough pulses to supply enough blood to the body. Chaotic rhythms occur where contractions of different parts of the heart are not synchronised and so pulse volume is reduced.
The pericardium is a strong sac that surrounds and supports the heart. Changes to the pericardium usually result in constriction of the heart, preventing it from filling properly between contractions. The right side of the heart (because it has thinner walls) is usually more easily compressed than the left.
Heart disease in older dogs is usually caused by damage to the heart valves or stretching of the heart muscle. Particular breeds of dog are more prone to certain types of heart disease.
What heart diseases are common?
The two most common types of heart disease in the adult dog are:
Valvular heart disease
Valvular heart disease is particularly common in Cavalier King Charles Spaniels (CKCS) but can occur in almost any breed. As a dog ages its heart valves may become worn and degenerate and therefore get more and more leaky. Instead of closing properly each time the heart pumps, the valves flop open allowing blood to move backwards as well as forwards through the heart chambers. This results in a reduced blood supply to the body.
Dilated cardiomyopathy (DCM) is a form of heart disease most commonly seen in large and giant breeds, particularly Dobermann pinschers, Great Danes and Irish Wolfhounds. Some spaniels are also affected and it could rarely affect dogs of any breed. The disease causes a stretching of the heart muscle walls so that the heart swells (like a balloon filled with water). The contractions of the heart muscle become very weak so blood is not pumped around the body effectively.
For more information on these forms of heart disease read the specific factsheet on each. In humans, heart disease is the result of damage to the heart muscle caused by blood clots (myocardial infarction) - this causes the signs of a heart attack. However, dogs do not get this kind of heart disease.
What are the signs of heart disease?
How do vets diagnose heart disease?
When your vet examines your dog he will use a stethoscope to listen to your dog's heart. If heart disease is present, your vet may hear a change in the heart sounds. The heartbeat may be fast (or occasionally slow), irregular or there may be an unusual noise (a murmur).
X-rays and ultrasound scans may also be used. X-rays may show that the heart is enlarged and ultrasound can be used to see whether the heart muscle and valves are working normally. An electrocardiogram (ECG), records the electrical activity that causes the heart muscle to beat and can be used to see if the beat is irregular.
Ask your vet to check a new puppy as soon as you get it and they will listen to its heart to detect any possible congenital heart problems. You may want to return the puppy to the breeder (if you are not already too attached to it) or, if possible, consider early correction of defects before signs of disease develop.
Can heart disease be treated?
How is heart disease treated?
In early stages of heart disease there may be no signs and your dog may just need to be checked regularly by your vet. If signs develop these can be treated. However, in most cases heart disease does get worse and treatment will only slow down the rate of disease progression. Such treatment includes:
- Changes to your dog's lifestyle, ie more controlled exercise.
- Drugs to improve the strength of the heart beat or change the heart rate (digoxin, pimobendan or antiarrhythmics).
- Drugs to remove excess fluid retention (ACE inhibitors and diuretics).
- Dietary changes may be recommended by your vet depending on the type of heart disease present.
Some congenital heart defects can be corrected by surgery. If your vet recommends surgery it is well worth considering. If the problem is corrected at an early stage (before any signs develop) it may be that your dog could be cured and never require any further treatment.