Let $f: M \to M$ be a diffeomorphism defined in a $d$-dimensional
compact boundary-less manifold $M$. We prove that
$C^1$-persistently expansive homoclinic classes $H(p)$, $p$ an
$f$-hyperbolic periodic point,
have a dominated splitting $E\oplus F$, $\dim(E)=\mbox{index}(p)$.
Moreover, we prove that if the $H(p)$-germ of $f$ is expansive
(in particular if $H(p)$ is an attractor, repeller or maximal
invariant) then it is hyperbolic.