2^0(34 Cardiac Dilatation. 



demands put upon it, and the less so as, owing to rapidly 

 succeeding contractions, some muscular fibers may tear. A 

 dilatation which has occurred in this manner either disappears 

 after a time, usually after a hypertrophy has developed in 

 the meantime, or it persists and leads to death, rarely within 

 a short time, although this has happened within a few minutes. 

 The trouble usually occurs most frequently in army and race 

 horses, and is designated by German authors as "Over-exertion 

 of the Heart," or "Acute Cardiac Insufficiency;" by French 

 authors, "Coeur force," "Coeur fatigue," "Surmenage." In 

 cattle and hogs the disease is not infrequent if these animals 

 are forced to do unusually severe muscular work (for instance, 

 while being driven to market) after long continued confine- 

 ment in the stable or after they are fattened. It is, however, 

 to be noted that in a number of such cases the heart muscle 

 ])ossibly had previously not been quite sound. (According to 

 de la Camp severe muscular work causes a dilatation only in 

 a heart which is already diseased.) 



In the majority of cases the basis for dilatation is pro- 

 vided by a disease of the heart muscle or of the arteries, also 

 by valvular anomalies, in which case the dilatation may develop 

 either acutely or chronically. Extensive degeneration of the 

 heart muscle may reduce the muscular force of the heart so 

 much that this organ cannot even overcome the normal blood 

 pressure. Of similar significance is myocarditis, which evi- 

 dently enters as a factor even more frequently than degenera- 

 tion of the heart muscle. Disease of the coronary arteries is, 

 in domestic animals, probably only rarely a basis for dilatation. 

 The same is true of tumors and parasites which may be found 

 in the heart. 



In the stage of insufficient compensation in valvular lesions, 

 the section of the heart which lies in front of the diseased 

 portion is dilated, while in diseases of the left venous ostium 

 the right ventricle is also dilated. The cause of this dilatation 

 will be discussed at greater detail under organic heart diseases. 



It is also as a consequence of cardiac weakness that dilata- 

 tion may occur as a sequel of cardiac li>7)ertropliy associated 

 with chronic nephritis. 



Anatomical Changes. The affected cavities of the heart 

 are larger than normal. The walls are flabby, so that the 

 opening is not patent when an incision is made on autopsy. 

 If the size of the heart was normal before the development 

 of the dilatation, the walls are thinner in proportion to the 

 degree of dilatation. If the disease has lasted for some time, 

 there occurs an atrophy of the muscles, which may be so ex- 

 treme that the visceral layer of the pericardium comes into 

 opposition to the endocardium (Dilatatio passiva). If, on 

 tlie other hand, the dilatation has developed in a heart that 

 had previously become hypertrophied, the wall of the dilated 



