It is certain that very considerable changes may take place in the muscular structure of the heart without any symptoms at all being apparent. When, however, the changes are such as to disturb materially the function of the organ, the disease is rendered apparent by very obvious signs, afforded in the first instance by a physical examination of the chest. If the enlargement be due to hypertrophy, the impact of the organ against the walls of the chest will not only be increased in intensity, but it will be felt over a much greater area than normal when the open hand is placed over the region of the heart. Moreover, the area of the dull sound commonly invoked by percussion is extended in proportion as the heart is enlarged, and this is the case whether the enlargement arises from hypertrophy or from dilatation, or both combined. There is, besides, more or less palpitation, especially under circumstances of exertion and excitement.

The usual recommendations to avoid excitement and fatigue are given when the disease is diagnosed, but as a matter of course, unless it is in such a stage that the rest that would be necessary need only be temporary, the animal is rendered perfectly useless, and might as well be destroyed. In fact, this alternative appears to be the reasonable one in all cases in which the disease is indicated by marked symptoms. For example, when an animal affected with a large heart - whether it consists in simple hypertrophy or only dilatation, or of the two conditions together - suffers from increased respiration when at rest, and to a greater extent during exertion, with the addition of staggering, attacks of vertigo, trembling, sometimes convulsions, and frequently derangement of the digestive organs, leading to loss of condition, emaciation, and anaemia, it may be concluded that the chances of recovery are so remote that it is not worth while to attempt any treatment.