Directional differences of impulse spread in trabecular muscle from mammalian heart

Trabecular bundles from the right ventricle of calf hearts were used. Electrical properties measured by the application of longitudinal current were compared to those measured by the application of transverse current. 2. The following data were obtained on the basis of classical cable analysis: (i) a ratio of 3-0 for longitudinal to transverse conduction velocity, (ii) a ratio of 3-6 for intra- to extracellular longitudinal resistance, (iii) a ratio of 12-6 for intra- to extracellular transverse resistance, (iv) a ratio of 9-4 for intracellular transverse to intracellular longitudinal resistance, (v) a ratio of 2-7 for the extracellular transverse to the extracellular longitudinal resistance. 3. The disparity in conduction velocity could be explained on the sole grounds of differences in the resistivity of the intracellular and extracellular paths for current flow in the two directions, confirming theoretical predictions. 4. The value of the transverse internal resistance can be accounted for on the ground of frequent branching in a three-dimensional network. There is no need to make the additional assumption of current flow through lateral low resistance pathways between parallel fibres.