Aim: Immunosuppression has evolved since the first successful orthotopic heart transplant 50 years ago. Currently, calcineurin inhibitors lie at the focal point of the immunosuppressive regimen. However, these drugs exhibit a variety of side effects, including hyperglycaemia. This in turn compounds the risk of cardiovascular disease. There is conflict around which calcineurin inhibitor, tacrolimus or ciclosporin, is more likely to induce diabetes. Methods: A retrospective analysis of data from 52 patients who had received a heart transplantation at the Scottish heart transplant unit between January 2011 and August 2017. All patients received a combination immunosuppressive regimen consisting of mycophenolate mofetil, corticosteroids and either tacrolimus or ciclosporin. Fasting glucose... levels were compared every 3 months after transplantation for a year. HbA1c was collected and compared at one interval during follow-up postoperatively. Statistical analysis was achieved using Students t-test for continuous variables and Chi-squared test for categorical variables. Results: The drug regimens remained unchanged in the two cohorts over the study period. The fasting glucose of tacrolimus treated patients was higher over the 12-month period compared to ciclosporin treated patients (7.3 ± 1 vs. 5.9 ± 0.5, P = 0.017). The results were significantly higher in the tacrolimus group at 9 months (P = 0.013). In contrast to these findings, HbA1c of the tacrolimus group was lower than the ciclosporin group, although there was no significant difference (38 ± 11.4 vs. 43 ± 1.3, P = 0.104). Conclusion: This study suggests a relationship between tacrolimus and rising fasting glucose among heart transplant population. However, a longer follow-up and control of confounding variables is required to denote the long-term impact of immunosuppression related diabetes in heart transplant patients.