  Based on the derivation of the macroscopic Maxwell's equations by spatial
averaging of the microscopic equations, we discuss the electrophysiology of
living organs. Other methods of averaging (or homogenization) like the bidomain
model are not compatible with Maxwell's theory. We also point out that modeling
the active cells by source currents is not a suitable description of the
situation from first principles. Instead, it turns out that the main source of
the measured electrical potentials is the polarization charge density which
exists at the membranes of the active cells and adds up to a macroscopic
polarization. The latter is the source term in the Laplace equation, the
solution of which gives the measured far-field potential. As a consequence it
is the polarization or dipole density which is best suited for localization of
cardiac arrhythmia.
