  We show that lepton-pair production in Virtual Compton Scattering offers,
through interference with the well-known Bethe-Heitler process, a sensitive
probe to learn the longitudinal response of resonances and the electromagnetic
nucleon form factors. This interference can be measured directly in terms of an
asymmetry. The role of off-shell effects in the N-N-$\gamma$ vertices is
investigated as well. An additional N-N-$\gamma -\gamma$ contact term in the
amplitude, included to ensure gauge invariance of the model, cancels a
substantial part of the off-shell effects.
