Rare and Suppressed Decays of $B^{0}_{(s)}$ Mesons with the ATLAS Detector

The large amount of Heavy Flavor data collected by the ATLAS experiment at the LHC is potentially sensitive to New Physics, which could be evident in processes that are naturally suppressed in the Standard Model. The most recent results for 4.9 fb$^{-1}$ of ATLAS data on the search for the rare decay $B^0_s \to \mu^+\mu^-$ are presented, as well as results of the angular analysis of the semileptonic rare decay $B^0 \to K^{*0} \mu^+\mu^-$ with $K^{*0} \to K^+\pi^-$, extracting the angular distribution parameters $A_{fb}$ and $F_L$. The accuracy obtained from data collected in 2011 is comparable to the best previous measurement in the region $q^2(\mu^+\mu^-) > 16$ GeV$^2$.