192 MANUAL OF EQUINE MEDICINE. 



is to be remembered that, in disease of the left side, the 

 right side may soon become disordered in consequence. 



In the horse, the mitral and aortic valves are more 

 specially liable to be diseased. In many instances both 

 valves are involved simultaneously. Probably the commonest 

 form of valve disease met with in the horse is aortic obstruc- 

 tion and mitral regurgitation. During auscultation, if we 

 are in doubt whether a murmur occurs during the systole 

 or diastole, we may feel the pulse at the jaw or fore-arm 

 while we listen. If the murmur is systolic, it will of course 

 be heard at the same time, or nearly so, as the pulse heat 

 is felt; if diastolic, it will be heard hetiveen the heats of the 

 pulse. 



Mitral Regurgitation. — At each systole of the left 

 ventricle blood flows back or regurgitates into the left auricle. 

 The pulmonary circulation thus becomes overloaded, and is 

 subjected to increased pressure. This difficulty is met, for a 

 time, by compensating hypertrophy of the right ventricle. 

 Hence, during this stage there are no symptoms of ill-health, 

 though there is not unfrequently difficulty of breathing 

 during exertion. After a time the hypertrophy of the ven- 

 tricle gives way to dilatation. Thus the engorgement and 

 tension of the pulmonary vessels is increased and reflected 

 back through the right side of the heart to the systemic 

 veins, which now also become overloaded, just as they do 

 from the first in cases of disease of the valve of the right side. 

 In consequence of the mitral regurgitation being no longer 

 compensated for by increased force of the right ventricle, the 

 aorta now becomes under-filled. 



Hence symptoms of systemic venous congestion follow. 

 Pulmonary complications with cough are sometimes present, 

 the breathing is disturbed, and there is severe dyspnoea 

 when the horse is much excited or during severe exer- 

 tion. 



