5.5.2 Clinical signs
The clinical signs seen in animals with a VSD depend on the haemodynamic effects of the defect. Large defects will result in volume overload early in life and CHF may be the presenting sign. Tachypnoea and dyspnoea may be noted and may be directly due to pulmonary oedema, or to pneumonia developing as a complication of pulmonary oedema. Other animals with less severe disease may not be noticed to be abnormal until it is found that they have difficulty in keeping up with their dams at pasture, or that they have a reduced exercise tolerance compared with other foals. Often a murmur is detected in foals as an incidental finding when they are examined for other purposes. Some animals behave quite normally initially and a significant murmur is only detected4ater in life when the horse shows signs of reduced exercise tolerance or is examined for another reason. This usually occurs at the start of an animal's athletic career. However, VSDs have been detected well into adult life, particularly in horses which do not perform arduous athletic work.