The natural result of this is, that diseases of remote structures or distant organs may so adversely influence the heart as to lead to indications which may easily, although incorrectly, be ascribed to derangement of the central organ itself; on the other hand, disease of the heart expressing itself by detectable alterations in its own sounds and movements is responsible for various forms of disturbance which occur in the digestive organs, liver, kidneys, or lungs, or some other parts. At the same time, it is thoroughly well recognized, as a fact about which there is no question, that grave structural and functional disturbance may affect the heart without leading to any manifestation at all which can be recognized as relating to that organ. In other words, an animal may die suddenly from heart-disease the existence of which had never been suspected during its life.
Among the symptoms which are frequently referred to disease of the heart are those which are described as subjective - that is to say, sensations which originate in the consciousness of the individual, such as pain, either continual or spasmodic, oppression in the chest, momentary stoppage or disturbance in the movements of the heart, dizziness, palpitations, and sinking. That these sensations, which are realized by the patient, are usually attended with extreme distress and apprehension will be readily understood, although it is a fact that all these clinical signs common in heart-disease may be experienced without any disease of the heart itself being present.
From the risk of error due to the existence of subjective symptoms, which would be usually classed under the head of extreme nervousness on the part of the subject, the veterinary surgeon is absolutely free. His patients either have no nervous apprehensions in regard to the state of their hearts or other organs, or, if they have, do not possess the means of expressing them in an intelligible manner.
Admitting, as must be the case, that disease of the heart of the horse is not so uncommon as it has been considered to be, the important question arises as to the best method of examination, for the purpose of detecting any obscure symptoms, which may be sufficient to direct the attention to the condition of the heart and the vessels immediately proceeding from it.
At the commencement it must be distinctly understood that while the veterinary surgeon is not subject to the risk of making an incorrect diagnosis in consequence of subjective symptoms or sensations which the horse cannot declare, he has to incur an equally prominent risk of arriving at a wrong conclusion in consequence of the derangement of the heart leading to disturbance of some other organs. The respiratory organs are, of course, most likely to be acted on. Any serious derangement of the central organ of circulation must necessarily interfere with the cirdilation of blood through the lungs; anything which leads to excessive contraction of the right ventricle, by which the blood is forced into the lungs directly, or any interference with the action of the left side of the heart arising from deficient contractile power or mechanical obstruction in the passage of blood through the left auricle or ventricle, would naturally induce a state of engorgement of the vessels, or congestion of the lungs, which would be indicated by symptoms which the veterinarian recognizes without difficulty. The breathing would become rapid and oppressed, the surface of the body would very quickly become cold, and from other signs the examiner would very quickly diagnose congestion of the lungs. The affection may be sufficiently severe to justify him in calling it pulmonary apoplexy. Such a diagnosis would be in effect strictly correct, although it may leave out of consideration altogether the real cause, viz.: the blocking up of the vessels of the lungs with stagnant blood, not on account of any derangement of the respiratory organs themselves, but entirely owing to the circumstance that the heart is in such a condition that it is incapable of carrying on the pulmonary circulation.
It does not follow that the congestion of the lungs arising from defec-tive action of the heart should take place suddenly to such an extent as would lead to any serious disturbance in the breathing, or justify the diagnosis of pulmonary apoplexy. Any mechanical difficulty affecting the circulation of blood in the lungs, whether arising from some impaired action of the heart or from any other interference, would lead to attacks of difficult breathing, cough, sometimes rupture of small vessels followed by bleeding from the nostrils, noises in respiration when it becomes at all hurried, sudden attacks of spasm, and in some cases a condition of the breathing which may lead to the impression that the horse is suffering from broken wind. Attacks of indigestion, and even gradually increasing emaciation, representing that state of the system which is expressed by the horseman's term " bad condition", are all indications which may be really consequent upon functional or structural derangement of the heart, although there may be no symptoms which specially direct attention to it.
As disease advances, more striking symptoms become evident. The wasting may be associated with dropsical effusions in the lower extremities and also along the inferior part of the abdomen, and there may be also more serious forms of dropsical effusion into the heart-sac (pericardium), the cavities of the chest, and abdomen. Chronic derangement in the central organ of circulation also leads to nervous derangement, in which the brain is commonly implicated. In the human subject, under these circumstances, the symptoms are easily recognized. The patient complains of frequent or even constant headache, with a feeling of fulness and heat about the head, rushing noises, throbbings, flushing of the face, giddiness, sleepiness, irritability, impairment of the intellectual powers, or actual mental derangement, disturbance of vision, movement of bodies before the eyes, twitchings in the extremities, and attacks of faintness.