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Electrical impedance of a bullfrog ventricle was recorded epicardially by the V-I method and the bridge method together with an electrocardiogram (ECG) and a contraction curve, in terms of shortening. Impedance change during one cardiac cycle of a contracting ventricle corresponded completely to the contraction curve in its time course: impedance decreased during systole and attained minimum at the peak of contraction, and the durations of both curves were almost identical. The ratio of impedance just before T-wave to that just after R-wave (|ZT|/|ZR|) of an in situ heart was increased when the ventricle contracted isovolumetrically by means of mineral oil: the ratio was far less than 1.0 in control ventricle, while it was more than 1.0 in oilfilled one (2/3 cases). Upon isometric condition or treatment of cadmium the motion restricted ventricle caused an increase in the impedance ratio (|ZT|/|ZR|) to higher than 1.0, as in the case of oil-filled ventricle. The epicardial recording of ventricular impedance seems to consist of two components: contraction (shortening)-dependent impedance change and contraction (shortening)-independent impedance change, which reflects the membrane activity. Vigorous contraction will probably mask the latter and reveal only the former.

An impedance locus consisting of two superimposed semicircular arcs was revealed on the abdominal skin of the bullfrog. The decrease of skin resistance upon epidermal application of Cd (2 mM), which was related to Na active transport, proved to be due solely to the reduction in the size of the high frequency arc.