  The existence of a second Higgs doublet in Nature could lead to a
cosmological first order electroweak phase transition and explain the origin of
the matter-antimatter asymmetry in the Universe. We obtain the spectrum and
properties of the new scalars $H_0$, $A_0$ and $H^{\pm}$ that signal such a
phase transition, and show that the observation of the decay $A_0 \rightarrow
H_0 Z$ at LHC would be a `smoking gun' signature of these scenarios. We analyze
the LHC search prospects for this decay in the $\ell \ell b\bar{b}$ and $\ell
\ell W^{+} W^{-}$ final states, arguing that current data may be sensitive to
this signature in the former channel as well as there being great potential for
a discovery in either one at the very early stages of the 14 TeV run.
