Heart Failure

The most common heart condition in horses is dysfunction of the heart valves and the animal will usually show no symptoms, other than a murmur, and monitoring is all that is required. The reason for there being no signs of heart failure is because of the body’s ability to compensate for the changes, however, as the condition deteriorates the body is unable to compensate any more and signs of heart failure may be seen. Any horse showing signs of heart disease should not be ridden to ensure that the rider’s safety is not at risk.

Signs of heart failure

  1. Left-sided heart failure: Horses will be weaker and have a reduced performance or even collapse. The mucus membranes are often pale and in severe cases there is dramatic weight loss. The heart rate will increase to 60-70 beats per minute, normal is around 40, and there may be arrythmias. There will be a reduction in the movement of blood from the lungs into the left hand side of the heart causing there to be a build up of fluid in the lungs. This will cause the affected animal to have an increased respiratory rate and increased lung sounds.
  2. Right-sided heart failure: As with left-sided heart failure the affected animal will be weak, have pale mucous membranes, a high heart rate and arrythmias. Horses will also have a reduction in the movement of blood from the body to the right hand side of the heart causing fluid to build up. This fluid most commonly builds up under the jaw, the underside of the chest and belly, the sheath and in the pleural cavity (around the lungs but not in the lung tissue itself as with left-sided heart failure).

Diagnosis

The clinical signs are normally very suggestive of heart failure, however, an ECG to monitor the heart rhythm and ultrasound scanning (echocardiogram) to visualize the heart and it’s movements are usually performed to assess the degree of the condition.

Treatment

Treating heart failure in horses can be uneconomic and unethical, however, in some cases heart failure can be controlled to enable the horse to breed successfully or enjoy early retirement. A diuretic, usually frusemide, is used in horses to reduce the accumulation of fluid. Vasodilators to reduce blood pressure and drugs to influence the contractility of the heart, digoxin, are also routinely used.