MicroRNAs (miRNAs) belong to a family of small non-coding RNAs that regulate mRNA translation. They are approximately 21 nucleotides long and are under the control of RNA polymerase II (Pol II) promoters. These promoters often contain a toxicologically significant enhancer region, which indicates miRNAs may play a role in responding to cellular stresses and gene changes following exposure to toxic substances.The current study was carried out to identify the potential use of miRNA profiling methods in determining a mechanistic based assessment of early stage toxicity in vitro. Quantitative real-time PCR (qRT-PCR, Applied Biosystems7900HT real-time PCR) was used to analyse the expression of mature microRNA (miR): miR-1, miR-21, miR-27a, miR-133a, miR-133b, miR-146a, miR-181 and miR-542 relative to the U6 small nuclear RNA in myocardium which was subjected to Doxorubicin treatment compared to naive vehicle control myocardium over an acute time period. In response to Doxorubicin (1µM) treatment, four miRNAs showed significant differential expression, shown in Table 1.This is the first study to show differential expression of miR-1, miR-133a, miR-133b, and miR-27a following exposure to Doxorubicin in the heart. We are currently investigating the potential of these miRNAs as biomarkers for drug induced cardiotoxicity.