Previous research has shown that informal caregiver burden can have deleterious effects on patient recovery; however, this relationship has yet to be investigated in patients undergoing coronary artery bypass graft (CABG) surgery. This study aimed to examine the impact of the change of caregiver burden from pre- to post-surgery on patients' mental and physical health after CABG surgery. Ninety patient-caregiver dyads were assessed one month before the surgery, two months and one year after the surgery. Caregivers completed the Oberst Burden Scale to measure caregiver burden. Patients completed the Beck Depression Inventory to measure depressive symptoms, a subscale of the Hospital Anxiety and Depression Scale to measure anxiety symptoms, the Short Form-12 health assessment to measure health-related quality of life, and the Coronary Revascularisation Outcomes Questionnaire to measure surgery symptoms. Hierarchical linear regression analyses were conducted to explore the association between change in caregiver burden and post-surgery patient outcomes. A greater increase in caregiver burden from pre- to two-months post-surgery significantly predicted higher patients' depressive symptoms (β = 0.179, p = 0.010), anxiety symptoms (β = 0.114, p = 0.017), reported post-surgery symptoms (β = 0.335, p = 0.008) and reduced physical health-related quality of life (β = -0.358, p = 0.003), after controlling for a wide range of covariates. These findings were not replicated at a one-year follow-up. These results provide insights into the impact of caregiver burden on patient distress following CABG surgery, supporting the idea of psychological support interventions for caregivers to increase patients' short-term recovery outcomes.