This study aims to evaluate the effectiveness of a rotating-leg prepper (intervention) compared with a rolled gauze bandage (control) in reducing pressure injury and preventing surgical site infection in the legs of patients undergoing heart surgery. The paired-matched, open, randomised controlled trial was conducted from September 2022 to July 2024. The participants were composed of the patient and the staff groups. Sixty patients were paired-matched to the intervention and control groups. Before painting the resting area with an antiseptic, the ankle presented non-blanchable erythema, which was recorded as a pressure injury. The intervention group showed significantly lower pressure injury (0% vs. 76.6%, p = 0.001) than the control group, with a relative risk of 5.29 (95% CI: 2.71–10.30). Both groups exhibited no significant difference in surgical site infection. However, the relative risk of surgical site infection in the control group was 2.03 (95% CI: 1.57–2.64). Thirty staff participants were purposively sampled to evaluate the effects of both leg lifting methods and assess their satisfaction with the leg prepper. The overall satisfaction with the rotating-leg prepper was 4.87 ± 0.22. Rotating-leg preppers can reduce pressure injury and prevent surgical site infections in patients' legs during heart surgery.