  In this paper we study the transition density and exponential ergodicity in
total variation for an affine process on the canonical state space
$\mathbb{R}_{\geq0}^{m}\times\mathbb{R}^{n}$. Under a H\"ormander-type
condition for diffusion components as well as a boundary non-attainment
assumption, we derive the existence and regularity of the transition density
for the affine process and then prove the strong Feller property. Moreover, we
also show that under these and the additional subcritical conditions the
corresponding affine process on the canonical state space is exponentially
ergodic in the total variation distance. To prove existence and regularity of
the transition density we derive some precise estimates for the real part of
the characteristic function of the process. Our ergodicity result is a
consequence of a suitable application of a Harris-type theorem based on a local
Dobrushin condition combined with the regularity of the transition densities.
