The vascular ring produced by the right subclavian artery was observed in four calves. In these cases the branch of the aortic arch was a brachiocephalic trunk originating from the proximal portion of the left aortic arch. In cases 1 to 3 the right subclavian artery was derived from the bisubclavian trunk originating from the brachiocephalic trunk, and the right subckavian aetery in case 4 arose from the brachiocephalic trunk as the first branch of the trunk.

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To investigate the characteristics of the heart rate fluctuations of sheep in a summer heat environment, experiments were performed on eight adult male and female Japanese Corriedale sheep in August (summer heat conditions) and in November (autumn control conditions). High respiration rates (ca. 200/min) and significant increases in the rectal, skin, and fleece temperatures observed at summer experiments indicated heat-stressed conditions of the animals. Mean R-R intervals were significantly lengthened in summer although the standard deviation and the coefficient of variation of R-R intervals were not significantly changed. In the results of spectral analysis of heart rate fluctuations by FFT, powers of the very low frequency (under 0.04 Hz, VLF) and the low frequency (0.04 to under 0.15 Hz, LF) bands were significantly inceased in summer. The power of VLF band expressed as the percentage to the total power was significantly increased in summer, but in contrast, that of the high frequency (0.15 to under 1.07 Hz) band was significantly decreased. It is presumed from the results that the amplitudes of the cyclic fluctuations in heart rate at the very low frequency and the low frequency bands are increased in a summer heat environment in relation to the adaptive thermoregulatory changes in the respirocirculatory functions.

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A 35-day-old gloden retriever, showing unthriftiness and exercise intolerance was diagnosed to have patent ductus arteriosus and subaortic stenosis based on echocardiography, cardiac angiography and cardiac catheterization. The echocardiography indicaed that the pressure gradient between the left ventricle and aorta was 130 mmHg. First, the ligature of arterial duct was conducted. The clinical symptom improved during 3 months after operation. Thereafter tachypnea gradually became prominent and the pressure gradient became up to 216 mmHg. The baloon dilation of stenosed aortic valve was conducted. The patient died 30 hours after the operation.

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A 10-month-old, 8.5-kg female intact Shiba dog was referred to the Azabu University Veterinary Teaching Hospital for further examination of congestive heart failure. At the time of first presentation, the dog appeared thin and mildly depressed. A Levine grade V/VI systolic ejection murmur and III/VI regurgitant murmur were heard loudest with point at the heart base of the left side and at the right sternal border, respectively. Radiography revealed dilatation of the main pulmonary artery, and enlargement of the right atrial and biventricular. Echocardiography demonstrated the ventricular septal defect (VSD) and pulmonary valvular stenosis (PS) with right ventricular hypertrophy.
Pulmonay artery banding is one of the treatments for VSD. The hemodynamic conditions of the present case resemble those of a VSD case with pulmonary artery banding. Because obvious hemodynamic changes have not been noticed for about 1 year, the shunt rate of VSD seems to be appropriately controlled by PS. However, although PS may prevent left heart failure caused by VSD, progressive right heart failure may be gradually advances. Therefore, complete surgical correction with pulmonary bypass is necessary before right heart failure advances.

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