The ATLAS heavy-ion program utilizes heavy-flavour hadrons to probe the hot, dense matter formed at the LHC. Quarkonium measurements have been performed in pp, p+Pb and Pb+Pb systems to study medium effects. The Pb+Pb results show a strong suppression of charmonium productions in more central events. Proton-lead interactions show little modification of the 1S charmonium state, but seem to indicate a centrality dependence of the 2S state. Upsilons have been studied in p+Pb and are found to show decreasing behaviour in more central collisions. Inclusive muons with pT above 4 GeV have been studied to provide insight on open-flavour production, and are found to be strongly suppressed in Pb+Pb collisions with a substantial and significant elliptic flow signal. Muon-hadron correlations have also been studied in the 2016 [see formula in PDF] = 8.16 TeV p+Pb data. There are clear indications of a near-side ridge, suggesting that similar mechanisms may be relevant for both the small and large systems.