Patients with pre-operative renal dysfunction are at increased risk of developing cardiac surgery associated acute kidney injury (AKI) but a proportion of patients with normal kidney function will also be affected. Studies show that patients developing AKI post cardiac surgery have a poorer long term prognosis, even if their kidney function subsequently returns to normal However, the cause for this is not currently understood. We postulate that a unifying mechanism makes such patients more susceptible to developing post-operative AKI and of having an overall worse long term prognosis. We suggest that this mechanism is reduced regenerative capacity of tissues. To test this hypothesis we will measure several markers of cell senescence and aging including telomere length, telomerase activity, and DNA methylation status.