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 scalar
s $H_0$, $A_0$ 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 $ell ell bbar{b}$ 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.
