Acute kidney injury (AKI) complicates over 25% of cardiac surgical procedures where it increases mortality up to fourfold. The incidence of AKI is increasing, the pathogenesis is poorly understood, current diagnostic tests lack specificity and sensitivity, and there is no effective treatment. Improving outcomes in patients at risk of AKI has recently been defined as an NHS priority. The primary aim of this study is to determine how plasma derived microvesicles (MV) or more specifically MV associated microRNAs (miRNA) regulate survival and signalling in post cardiac surgery AKI. The study involves a clinical and experimental research project that will combine laboratory analyses of circulating MV and miRNA from clinical studies. The study will specifically consider how MV and miRNA alter inflammatory signaling in kidneys after cardiac surgery, how these are modified by important clinical risk factors, and whether they may serve as early biomarkers of injury.