406 HEALTH AND DISEASE 



Obstructive disease of the aortic valves gives rise to thickening of the walls 

 of the left ventricle, while the same condition of the pulmonary valves 

 would similarly affect the right. 



Enlargement of the heart may arise from increase in the development 

 of the muscular structure (hypertrophy of the muscular walls), or from 

 dilatation of the cavities from extra pressure from within. But it is pretty 

 generally recognized that the same obstruction which gives rise to hyper- 

 trophy will also occasion dilatation of the cavities, hence it is found that 

 both conditions usually exist to a greater or less extent at the same time. 



The heart of the horse, which in a normal condition weighs aljout 

 seven or eight pounds, may be increased in this disease to twelve or 

 more pounds. 



Hypertrophy and dilatation are much more common in the left ventricle 

 than in the right, for the reason that the valves of the former are moie 

 liable to sprain and disease than those of the latter. It will be remem- 

 bered that the left ventricle sends the blood over the entire body, while 

 the function of the right is confined to distributing it over the lungs. The 

 work entailed in the former act being so much greater than that of the 

 latter, the chances of obstruction to the blood flow are correspondingly 

 increased. Thus the aorta, the vessels of the kidneys or the liver, or those 

 of one or more of the various organs of the body, may by disease become 

 narrowed, and tend to obstruct the circulation, which in time the heart 

 would attempt to overcome, and its increased effort would have the effect 

 which follows all muscular work, of sooner or later causing thickening of its 

 walls. If the obstruction continued, or for any reason became worse, 

 dilatation of the heart would follow hypertrophy. In these cases the valves 

 which guard the orifice are required to stretch in order to fill up the still 

 larger opening, or they sprain and become diseased. 



It does not necessarily follow that because the heart is enlarged 

 its walls should be thickened. This will fi-equently depend upon the 

 amount of dilatation which it has undergone. In some cases the walls 

 are much thinner than normal owing to the hypertrophy not having 

 kept pace with the dilatation. 



Symptoms of Enlarged Heart. — 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 



