  We prove the existence of strong time-periodic solutions to the bidomain
equations with arbitrary large forces. We construct weak time-periodic
solutions by a Galerkin method combined with Brouwer's fixed point theorem and
a priori estimate independent of approximation. We then show their regularity
so that our solution is a strong time-periodic solution in $L^2$ spaces. Our
strategy is based on the weak-strong uniqueness method.
