3.2.4 Performance history
One of the best indicators of the significance of heart disease is its effect on athletic performance. If a horse has had a problem, for example a relatively quiet murmur of mitral regurgitation, for a long period of time, but has a good perrecord, it is quite likely that the significance of the condition is minor. However, if athletic performance has been disappointing, then it is more likely that the valvular regurgitation is significant and that this is responsible. Nevereven when mitral regurgitation is present, other causes of poor perforshould also be considered (see section 8.2.4). It is therefore important to find out whether the horse has ever performed well, or whether the performance level has dropped off in the recent past. For example, it may be possible to infer that the onset of a problem such as atrial fibrillation was likely to be at the time of the deterioration in performance. This may be helpful in advising about the chances of successful treatment (see section 7.8.5). There are occasions on which successful sale of an animal may depend on a satisfactory working record after the point at which the problem was detected. However, the value of a performance history depends on the horse performing at a level which is similar to that which it is intended to do in the near future. For example, it may be difficult to establish the duration of atrial fibrillation in an animal which has been rested for a prolonged period.