  Measurements of deeply virtual Compton scattering (DVCS) made at HERMES using
27.6 GeV $e^\pm$ beams and various internal polarized or unpolarized gaseous
targets are discussed. Results are reported on the transverse target-spin
asymmetry (TTSA) associated with DVCS, extracted from data accumulated in
2002-2004 with the $e^+$ beam on a transversely polarized hydrogen target. TTSA
amplitudes leading in twist and $\alpha_S$ are given as a function of $-t$,
$x_B$ and $Q^2$ in the kinematic range $|t|<0.7$ GeV$^2$, $0.03<x_B<0.35$ and
$1<Q^2<10$ GeV$^2$. Theoretical predictions based on a phenomenological model
of generalized parton distributions (GPDs) agree with the experimental results.
With additional statistics accumulated in 2005, one may constrain the $u$-quark
total angular momentum in the nucleon within this model.
