In order to study the function of the septomarginal trabecula (MB); four calves were subjected to the experimental cutting of MB and observed electrocardio-graphically and morphologically. Moreover, the beating heart was observed in another calf by echocardiography.
From the results of echocardiography of the beating heart and radiographic and macroscopic observations of the operated hearts, the MB was not found to tend to prevent of right ventricle from overdistention.
In all the calves the main stems of the right limb of the atrioventricular conducting system were sectioned by cutting the MB. The durations and wave forms of QRS in A-B lead remained unchanged after the cutting of the MB. Two of these showed changes in wave form of QRS in the standard limb, augmented unipolar limb, and unipolar chest leads after the cutting.

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The arterial and intracardiac blood pressures of the left and right hearts were measured to analyze several cardiac parameters in twelve adult beagle dogs. An experiment was performed under anesthesia of fluothane. Catheters were inserted into the left and right hearts through the common carotid artery and jugular vein under fluoroscopy. Each pressure wave was recorded on a visigraph and a data-recorder with a strain gauge pressure transducer. Values of cardiac parameters were analyzed with a signal processor.
In the left heart, each pressure was measured systolic aortic pressure (Ps), diastolic aortic pressure (P_D), mean aortic pressure (P_M), left ventricular end-diastolic pressure (LVEDP), left ventricular peak-systolic pressure (LVP_KS), left ventricular maximum dp/dt (LV max. dp/dt) and time to left ventricular maximum dp/dt (t-LV max. dp/dt).
In the right heart, each pressure was measured systolic pulmonary arterial pressure (PA_S), diastolic pulmonary arterial pressure (PA_D), mean pulmonary arterial pressure (PAM), right ventricular end-diastolic pressure (RVEDP), right ventricular maximum dp/dt (RV max. dp/dt) and right atrial pressure (RAP).
The results are as follows;
1) In the left heart, Ps was 111.0mmHg, P_D, 76.5mmHg, P_M, 87.7mmHg. LVEDP, LVP_KS, LV max. dp/dt, and t-LV max. dp/dt was 9.5mmHg, 113.5mmHg, 2608mmHg/sec and 64 msec, respectively.
2) In the right heart, PA_S was 24.6mmHg, PA_D, 10.2 mmHg, and PA_M, 14.7mmHg. RVEDP, RVPpks, and RV max. dp/dt was 5.0mmHg, 30.5mmHg and 552mmHg/sec, respectively. RAP was 4.1mmHg.
3) There were no significant differences in the value of any cardiac parameter between adult beagles and mongrel dogs.

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Electrocardiograms (ECG) were recorded from 83 clinically healthy dogs by computerized electrocardiography (CE). The results obtained are summarized as follows.
1) The diagnosis made by CE hardly coincided with the true diagnosis even when the chest unipolar leads and wave pattern were corrected to such extent that they might be similar to those of human beings.
2) The results of diagnosis by CE were low in reproducibility.
3) The heart rate determined by CE was reliable until it was 180 per minute. When it exceeded 180, a big error was noticed in it.
4) The smaller the amplitude, the larger the error between the amplitude determined by CE and that actually measured. The fluctuation of the basic line was also influenced considerably. The R and T waves of large amplitude were measurable.
5) Duration and interval determined by CE were almost always inexact, being longer than those measured actually.
6) It seemed necessary for the application of CE to animals for diagnosis not only to change the existing program but also to make improvement in various points.

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A diagnosis of ventricular septal defect (VSD) was made tentatively in a male rabbit 18 months of age of the Japanese White mixed breed weighing 1. 3 kg. It was based on the results of physical and hematological examinations, radiography, electrocardiography, and phonocardiography. Unfortunately, the animal died after suffering from a defect in left heart angiocardiography. Necropsy revealed that the animal had the membraneous type of VSD.

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