Author's reply: critical curvatures in the heart

The analyses made by A.T. Winfree regarding critical cardiac curvatures failed to take into account the influence of propagation fronts caused by boundary effects on the isotropic properties of cardiac tissue. The author did not recognize that the value for critical curvatures obtained by rescaling to anisotropy is not the same as that for critical curvatures that are theoretically present on either axis in the heart. Winfree's conclusions can have detrimental consequences on the design of small pacing electrodes for the cardiovascular system.