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 H0, A0, and H(±) that signal such a phase transition and show that the observation of the decay A0→ZH0 at LHC would be a "smoking gun" signature of these scenarios. We analyze the LHC search prospects for this decay in the ℓℓbb and ℓℓW(+)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 channel at the very early stages of the 14 TeV run.