Standard and augmented limb leads electrocardiograms were obtained from 11 healthy Caspian Pony. Recordings were analysed for rhythm, rate, electrocardiographic configurations, intervals and amplitudes. The mean intervals for the P, P-R, QRS and Q-T in lead II measured 0.077±0.014, 0.187±0.019, 0.078±0.026 and 0.441±0.043 sec, respectively. The mean heart rate of the Caspian Pony was 38.33 beats per minute.

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A study was carried out to clarify the distribution of the P, QRS and T electric axes in cats. In it, electrocardiograms were recorded by means of needle electrodes from 11 adult cats lying on the right side under nembutal anesthesia. The mean electric axes were calculated for Einthoven's triangle on the horizontal and sagittal plane. On the two planes, vectorcardiograms were recorded with a transient-memory apparatus and an XY recorder. The results obtained are summarized as follows.
1) The mean P, QRS and T electric axes on the horizontal plane formed an angle of 72.4, 81.4 and 63.6 degrees with the reference line to induce a mean voltage of 0.094, 0.415 and 0.121 mV, respectively.
2) The mean P, QRS and T electric axes on the sagittal plane formed an angle of 37.3, 41.7 and 43.9 degrees with the reference line to induce a mean voltage of 0.086, 0.575 and 0.187 mV, respectively.
3) The mean electric axes were in good agreement with the vectorcardiograms.
4) The mean QRS electric axis on the sagittal plane corresponded more or less to the direction of the anatomical cardiac axis.

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A five-year-old male Anglo-Arabian racehorse suddenly lost running speed during a race. Although he managed to complete the course, his race time was 6.1 seconds behind the winner. After the race, a veterinarian detected an irregular heart rhythm of unknown etiology. An electrocardiogram recorded on the 36th day after the race indicated the presence of atrial fibrillation. The horse was treated with quinidine sulfate by the aid of a stomach tube on the 53rd day after the race. First, he was given a test dose of 5 g of quinidine sulfate, but no side-effects of the drug appeared. On the next day, a therapeutic dose of 10 g of the drug was administered. When performed 105 minutes after the therapeutic dose, electrocardiographic examination revealed no atrial fibrillation and sinus rhythm was reestablished.

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Nine months old Shiba dog (Male) was referred to our Institute. The dog suffered from four episordes of syncopal attack during 6 to 8 months of age.
On auscultation, holosystolic regurgitant murmur was best heard along the right sternal border at the fourth intercostal space. The electrocardiogram (ECG) showed occasional second degree atrioventricular block and sinoatrial arrest. His bundle electrogram and atrial pacing revealed prolonged P-H interval but without sinus node abnormality. Angiocardiogram demonstrated membranous septal defect.
ECG of his parents and three littermates disclosed first degree atrioventricular block in his father and one of the littermates, therefore, we considered that this disturbance might be hereditary heart block.

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