204 THEORY AND PRACTICE 



volviiig only part of one. It alters the shape of the heart, which 

 has a more nearly round appearance when hypertrophied. The 

 left ventricle is the most likely to be involved, probably on ac- 

 count of the larger amount of work it has to do. The enlarge- 

 ment may Tbe due to the dilatation of the cavities or it may be due 

 to increased thickness of the walls. In draft horses both are 

 likely to occur together. Ossification of the valves may occur. 



Simple dilatation is dilatation of the cavities, principally the 

 right ventricle, without thickening of the walls. Sometimes even 

 a thinning of the wall of the right ventricle is seen. 



Simple hypertrophy is the condition in which the ventricular 

 walls are thickened but the cavities are normal in size. 



Eccentric hypertrophy implies both the thickened walls and 

 the dilated cavities. 



Concentric hypertrophy implies the thickened walls and the 

 contraction of the cavities. 



Hypertrophy with dilatation is by far the most frequent form 

 of cardiac enlargement. The heart may be three or four times 

 its natural size. 



Etiologv. — Long-continued, severe exertion always causes car- 

 diac enlargement. It is seen in fast horses, especially trotters 

 and pacers that have done hard campaigning for three or four 

 years, and aged hard worked draft horses. This hypertrophy 

 dves little or no inconvenience unless the animal is attacked by 

 some other disease, then he is more liable to succumb than if 

 he had a normal heart. Inflammatory diseases with high fever, 

 especially pneumonia, is liable to produce simple dilatation. The 

 concentric hypertrophy follows long continued over-exertion. The 

 horse usually dies from some disease aggravated by the weak 

 condition of the heart. 



Semeiology.— The heart in simple, eccentric and concentric 

 hypertrophy gives a powerful impulse at each beat; pulse full 

 and strong. In simple dilatation it gets weaker and weaker until 

 severe dyspnoea results. If the pulse is small and feeble at the 

 jaw we may conclude that there is some cardiac weakness, 

 probably simple dilatation. 



Treatment.— In simple dilatation and other cardiac weak- 



