  We study constraints on Left-Right Symmetric models from searches of
semileptonic decays of $D$, $D_{s}$, $B$ mesons, mediated by heavy neutrinos
$N$ with masses $m_N\sim $ GeV that go on their mass shell leading to a
resonant enhancement of the rates. Using these processes we examine, as a
function of $m_N$ and $M_{W_R}$, the physics reach of the recently proposed
high-intensity beam dump experiment SHiP, which is expected to produce a large
sample of $D_s$ mesons. We compare these results with the corresponding reach
of neutrinoless double beta decay experiments, as well as like-sign dilepton
searches with displaced vertices at the LHC. We conclude that the SHiP
experiment has clear advantages in probing the Left-Right Symmetric models for
heavy neutrinos in the GeV mass range.
