The hazardous consequences of heavy metal ions (HMIs) on human health necessitate the immediate need to probe fundamentally the interactions and cytotoxic effects of HMIs on humans. This study investigated the influence of five toxic HMIs (arsenic (As (III)), cadmium (Cd (II)), chromium (Cr (VI)), mercury (Hg (II)), and lead (Pb (II))) on human TNBC (HCC 1806) cell viability using optical microscopy, trypan blue dye-exclusion assays, and flow cytometry. The TNBC cells were exposed to varying concentrations of HMIs for 24 and 48 hours. We evaluated the influence of the concentrations and duration of HMIs exposure on TNBC cell viability. Light microscopy, cell viability assays, revealed that after 48-hour treatment of TNBC cells with 1 x 10-5 M of As (III), Cd (II), Hg (II), Cr (IV), and Pb (II) resulted in cell viabilities of 23%, 34%, 35%, 56%, 91% respectively, suggesting that As (III) has the greatest cytotoxicity (77% cell death) while Pb (II) showed the least (9% cell death). Furthermore, flow cytometry revealed that while Pb (II), As (III) and Cr (IV) had significant increases in cell death, Hg (II) caused a G1 arrest. Together, this study revealed that HMIs cause a differential cytotoxic effect on TNBC cells and suggest that they may have very different genotoxic targets and implications in their mutagenic potential.