Title: Increased Delayed Afterdepolarisation Susceptibility in Hypertrophic Cardiomyopathy Cardiomyocytes Under Exercise Conditions Background: Electrophysiological mechanisms underlying exercise as a potential arrhythmic trigger in hypertrophic cardiomyopathy (HCM) remain incompletely understood, while clinical exercise guidelines continue to evolve. This study aimed to analyse delayed afterdepolarisation (DAD) formation in cells affected by HCM ionic remodelling. Methods: Control and HCM action potential model populations were constructed by varying ionic conductance multipliers and calibrating models to experimentally reported ranges. Both populations underwent a DAD induction protocol consisting of fast pacing and beta-adrenergic stimulation, followed by a 10 second quiescent period. Results: HCM models showed more than double the DAD incidence of controls and longer trains of DADs, with longer DAD trains being associated with upregulated IKr conductance in the HCM population. Targeting the downregulated Na+/K+ pump in HCM notably reduced DAD incidence and the length of DAD trains. Conclusion: In conclusion, this study demonstrates a higher risk of DADs in human HCM cardiomyocytes under exercise conditions, compared to non-diseased cardiomyocytes.