The Screen-Well® cardiotoxicity library is a focused collection of 130 compounds with defined and diverse cardiotoxicity, including ion channel blockage, mitochondrial toxicity, arrhythmia, fibrosis, and many more. A variety of structurally and mechanistically different compound classes are included, as well as nontoxic controls. The compounds are dissolved in DMSO at 10 mM and aliquoted into deep-well plates. The library is an essential tool for predictive toxicology screening and assay development.