DISEASES or THE UEAIIT. — UYPEKTROPHY. 269 



a. Myocardium. 

 A. Ili/pertrophi/ of the Heart. 



§ 234. By hypertrophy of the heart we understand an in- 

 crease in the bulk of that organ, due to overgrowth of its 

 muscular coat. It may affect both ventricles equally ; it more 

 often affects one only, or chiefly. It is not an easy matter to 

 ascertain the existence of a moderate degree of hypertroph}'. 

 We are told to compare the thickness of the walls with the size 

 of the cavity. But their ratio varies with every variation in the 

 degree to which the heart is contracted. The size of the cavity 

 varies inversely as the thickness of its walls. We are never sure 

 whether the seeming increase in the thickness of the wall may 

 not be merely due to the heart being more firmly contracted. 

 Doubts of this sort meet us again when we try to find out if 

 the heart's substance is atrophied ; we have to be on our guard 

 against supposing a dilated heart to be atrophied merely because 

 its walls are thin. A power of quick and accurate judgment 

 with regard to moderate degrees of thickening and thinning of 

 the heart's walls can only be got by long practice. On the other 

 hand it is very easy to recognise hypertrophy in its extremer 

 forms. Next to the enlargement and the change in shape — a 

 change which is often very striking — our attention is roused by 

 the disproportionate increase in weight of the heart. The walls 

 of the hypertrophied organ are as stiff and hard as boards, so 

 that even after the blood has been entirely evacuated by incision, 

 they do not collapse, and cannot be easily bent in or out. Final 1}^, 

 the marked increase in thickness of the wall is made all the 

 more striking by the coincident enlargement of the cavity, since 

 hypertrophy is invariably associated with a certain degree of 

 dilatation. A large heart must needs have a large cavity. 



Tlie shape of the heart is characteristically altered when only 

 one of the two ventricles is hypertrophied. If we were to join 

 the left ventricle of an adult to the right ventricle of an infard, 

 the entire heart would appear to consist chiefly of the left 

 ventricle ; reversing the process, the right ventricle would pre- 

 ponderate in like manner. This exactly illustrates what happens 

 in unilateral hypertrophy of the heart. 



A heart with a hyi)ertrophied left cenirlclc (fig. 83) will 



