Background The utility and uptake of Del Nido cardioplegia in adult cardiac surgery is rapidly increasing. Cases with prolonged aortic cross clamp times necessitate multi dosing however an understanding of safe ischaemic times and definitive guidelines in this domain are lacking. Therefore, the aim of this study was to assess the safety and efficacy of our DNC strategy by comparing post-operative troponin profiles and clinical outcomes between del Nido and hyperkalaemic cardioplegia for cases with aortic cross clamp times of greater than 90 minutes. Methods A single centre, retrospective cohort study at Flinders Medical Centre and Flinders Private Hospital of patients undergoing composite cardiac surgery with a cross clamp time longer than 90 minutes. Data was prospectively collected from the Flinders Cardiac Surgery Registry from June 2014 to December 2022. A propensity matched (1:1) analysis was performed comparing patients receiving del Nido cardioplegia (n=194) to those receiving hyperkalemic blood cardioplegia (n=194). Primary outcome was the post-operative troponin release profile with clinical events reported as secondary outcomes . Results There was no difference in the peak or median troponin at 6, 12 and 72 hours nor number of patients with positive troponin profile post operatively between cohorts. There was no difference in clinical outcomes between groups with aortic cross clamp times of 90min which remained true in Sensitivity analysis extending out to 120min. The Del Nido cohort received less cardioplegia volume (p <0.001) and were more likely to return to spontaneous rhythm (p <0.002). Conclusion Del Nido cardioplegia for anticipated aortic cross clamp times of greater than 90min provided equivocal post operative troponin profiles and clinical outcomes compared to multidose hyperkalemic blood cardioplegia.