  We prove surface and volume mean value formulas for classical solutions to
uniformly parabolic equations in divergence form. We then use them to prove the
parabolic strong maximum principle and the parabolic Harnack inequality. We
emphasize that our results only rely on the classical theory, and our arguments
follow the lines used in the original theory of harmonic functions. We provide
two proofs relying on two different formulations of the divergence theorem, one
stated for sets with almost C^1 boundary, the other stated for sets with finite
perimeter.
