A Mechanocardiogrphic polygram (MCG) was recorded from 19 normal heifers and 21 dairy cows. Carotid arterial pulse (CAP) wave pattern and left ventricular systolic time intervals (STI) were studied.
1) The wave form of CAP in cattle was similar to that in human beings. All the important points (points of change in curve) were clearly demonstrated on the CAP.
2) There was a significant correlation (r=0.99, n=8) in the ejection time (ET) between the pulse waves recorded from MCG and CAP.
3) There was a high inverse relation between the heart rate and the electromechanical systole (QIIa) or ET which made it possible to calculate a QIIa index (QIIal) or ET index (ETI). The pre-ejection period (PEP) and the ejection index (ET/PEP) were reliable indices, because they were free from influence of the heart rate.
4) Comparison was made on QII aI, ETI, PEP and ET/PEP between the normal heifers and the dairy cows. ETI was significantly longer, PEP significantly shorter, and ET/PEP significantly higher in the latter than in the former.

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Two-dimensional echocardiography(2-DE) was performed on three dairy cows in which bacterial endocarditis was suspected. The 3 rd and 4 th intercostal spaces at the level of the elbou were chosen as acoustic windows. Dense vegetative echoes were seen on the mitral valve and the tricuspid valve in case 1, on the tricuspid valve in case 2 and on the pulmonary valve in case 3 by 2-DE. In addition to 2-DE, M-mode echocardiography was performed in the three cases to see the motion of the vegetation. Finally, a diagnosis of bacterial endocarditis was made from the results of 2-DE, M-mode echocardiography, clinical examinations, blood bio chemistry, ECG and PCG.

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Cows with dilated (congestive) cardiomyopathy (case 1), chronic large abscesses of the pericardium (case 2) and bovine leukemia with cardiac involvement (case 3) were examined, using M-mode and two-dimensional echocardiography. Case 1 was characterized by dilatation of four cardiac chambers with poor ventricular function. Case 2 revealed the existence of large pericardial abscesses accompanied by cardiac atrophy echocardiographically. The echocardiographic features of case 3 were symmetrically thickened ventricular walls due to leukemic infiltration of the myocardium. Besides, an abnormal mitral closure on the M-mode echocardiogram, indicative of an elevated left ventricular end-diastolic pressure was added to cases 1 and 2. Echocardiographic findings corresponded, to a certain degree, to pathological findings.

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Subendocardial Purkinje (P) fibers in the bovine heart were observed by scanning electron microscopy after removal of the endocardium or freeze cracking. Small branches from the left and right limbs of the atrioventricular conducting system were spread out, forming an irregular and delicate P network under the ventricular endocardium. P fibers forming strands of the network were roughly cuboidal, rectangular, or oval. They were branching cells with a diameter two to five times as long as that of the ordinary cardiac muscle fibers. The P fibers had few myofibrils and mitochondria. Their sarcoplasm was packed with a network of filaments which were not organized into myofibrils. They frequently communicated with ordinary cardiac muscle fibers through transitional fibers. A direct continuity was rarely observed between them.

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To elucidate the localization and arterial supply of the sinoatrial(S-A) node in the dog, 10 adult dogs (9-35 kg in body weight) were selected, at random, from among those necropsied in the Department of Veterinary Pathology, Tokyo University of Agriculture and Technology. By postmortem coronary arteriography, the heart was observed for the arterial supply to the S-A node by preparing a transparent specimen of the right atrium. Finally, the S-A node and its artery were examined histologically.
The S-A node, which seemed to have the shape of a cone, was located along the sulcus terminalis. It was approximately 12×3×1 mm in size. Its head or the base of the cone, laid at the junction of the cranial vena cava and the intermediate between the anteromedial and anterolateral wall of the right atrium. Its tail, or the apex of the cone, terminated in the middle part of the free lateral wall of the right atrium.
When the angiogram and transparent specimen was observed, the artery to the S-A node originated from both left and right coronary arteries in 8 of the 10 dogs, from the left artery in one dog, and from the right artery in the other dog. In addition, there were often interarterial coronary anastomoses in the S-A node area. As for the localization of the S-A node and its artery, the S-A node artery ran along the vicinity of the node(extranodal artery). In a few dogs, a part of the node had an intranodal artery which was regarded as a type of so-called central artery.

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Cardiac structures were measured in 98 dogs to obtain the normal structure values of the heart. There was no difference in the measured values between male and female dogs. Puppies had a significantly higher heart-body weight ratio (12.6±6.33 g/kg) than the adult dogs. There were no significant age differences, however, in any other measured value. Such value was independent of sex, age and body weight. There was a tendency that the circumference of the left cardiac valves was shorter than that of the right (Pa>Ao, Tri>Mi).
The left and right ventricular wall increased in thickness at almost the same speed, because there were no significant changes in the right ventricle and the ventricular septum ratio (RV/IVS) (0.50±0.12-0.67±0.16) or the ventricular septum and the left ventricular ratio (IVS/LV) (0.88±0.09-1.33±0.18).

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Electrocardiographical changes were studied in growing beagles with the following results.
1. The variable measured values of ECG were synchronized with adult values after 9 months of age.
2. The QRS eletricai axis was markedly shifted to the right (-152°) at 2 days of age. It shifted back counterclockwise at 3 months of age to be in the normal range of the adult dog. During this process, the QRS electrical axis shifted temporarily further to the left from the normal range.
3. A number of individuals showed negative waves at 1 month and 2 weeks of age probably due to the influence of the vagal nerve.
4. Respiratory arrhythmias appeared at 1 month and 2 weeks of age.
5. Electrical alternans appeared in dogs during growth.

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The existence of a circadian rhythm on the electrocardiogram was studied in 20 dogs. Statistically, it was confirmed in 7 measuring items: heart rate, P-R interval, Q-T interval, P wave amplitude, P wave duration, R wave duration, and S wave duration.
From 8: 00 a.m. to noon, P, R, and S waves showed tendencies to increase in interval and to decrease in voltage. From 8: 00 p.m. to midnight, however, they tended to be short in duration and to increas in voltage.
The average of circadian rhythm in the 20 dogs moved to a normal value. In individual dogs however, it was not a little lear that each measuring item moved both internally and externally from a normal range.

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In order to elucidate whether or not changes in heart rate, arterial pressure and arterial blood gases and pH were directly related to the genesis of bifid T wave, some experiments with adult male Wistar rats anesthetized with urethan (1.25 g/kg, i.p.) were performed under normothermia, before and after the procedure of hypothermia and the administration of isoproterenol. The configuration of T wave was not markedly changed by the atrial-paced increase in heart rate in normothermic rats. Changes in arterial pressure, arterial blood gases and pH before and after cooling and the administration of isoproterenol were not in accordance with the appearance of the bifid T wave. From these results, it was concluded that the respective changes in heart rate, arterial pressure and arterial blood gases and pH were not directly related to the appearance of a bifid change of T wave.

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Myocardial infarction with mitral regurgitation was diagnosed in a 13-year-old English setter. At the first medical examination, systolic murmurs in the mitral area were recorded by the phonocardiogram. Ventricular premature contractions and fushion beats were recorded on the electrocardiogram(ECG). After ECG examination, the dog was treated immediately with the antiarrhythmic drug.
On the first day of treatment, the dog had a good response to the treatment. Clinical signs and ECG findings were recovered. On the 6th day ventricular tachycardia occurred. On the 7th day, the dog had no response with any antiarrhythmic drug and died of ventricular arrhythmia.
Postmortem examination revealed thrombus in the cranial descending coronary artery (ventral interventricular branch of the left coronary) and left circumflex coronary artery (circumflex branch). Ischemic changes were also observed in the left anterior papillary muscle. The mitral valve leaflets were severely thickened. Calcification was seen in the sinus of Valsalva.

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