Auricular Excitability of the Normal Dog Heart *

Experiments heretofore designed to examine the response of the heart to electrical stimulation were in general carried out under conditions which did not allow the heart to function in its normal environment. Most experiments were performed on isolated or open chest preparations in which factors of heat loss, CO2 escape, and evaporation were difficult to control. Furthermore, the hearts were not usually allowed to beat spontaneously but instead were driven by an external stimulus.'3 In 1952 Sikand, Nahum, Levine, and Geller1' by means of a cylindrical electrode passed into the heart through the chest wall were able to establish the excitability cycle of the dog ventricle in its normal physiological environment. Sufficient differences in the ventricular response of such a heart to electrical stimulation from previously reported studies made it desirable to determine whether the auricle in its normal state, like the ventricle, might exhibit an excitability curve different from that previously described.' The method used by Sikand et al. to study the problem in the ventricle was not applicable in the case of the auricle since it is not accessible to blind insertion of the cylindrical electrode. Accordingly, the electrodes were prepared by the method of Delgado and Sikand' and implanted aseptically onto each auricle by a slight modification described elsewhere.'