The passive and active electrical parameters of frog ventricular myocardium have been measured. 2. The cytoplasmic resistivity has been determined by following changes in the resistance of a micro-electrode on penetration of a cell. 3. Unidimensional cable analysis using direct and alternating currents revealed the presence of a single time constant attributed to the surface membrane. 4. Longitudinal impedance measurements indicate that a second time constant is present in the intracellular pathway. 5. The results indicate that the resistance between cells is low so that action potentials can propagate from cell to cell by local circuits. 6. A three-dimensional cable analysis has also been carried out and compared to a simplified mathematical model which is presented in an Appendix and which closely approximates the experimental situation.
