BACKGROUND: As open-heart surgery can be stressful for the patient and their family, the objective of this study was to generate knowledge on how to support families in relation to open-heart surgery based on important situations. AIM: The aim was to explore and describe the experiences and actions of important situations of family involvement as expressed by family members of patients who underwent elective open-heart surgery in Sweden. METHODOLOGICAL DESIGN AND JUSTIFICATION: The critical incident technique used is a qualitative method appropriate for identifying issues relating to clinical problems. ETHICAL ISSUES AND APPROVAL: Ethical approval was obtained from the Swedish Ethical Review Authority. Allowance was made for the unexpected presence of the patient. RESEARCH METHODS: Individual interviews with 29 family members of patients who underwent open-heart surgery in Sweden in 2023 were analysed using the critical incidence technique, as applied in nursing and healthcare sciences. RESULTS: The family members experienced being-or not being-seen as significant and were fearing the loss of normal life in relation to open-heart surgery. Actions taken during important situations were building confidence to relinquish control and relieving burdens to improve well-being. CONCLUSIONS: Family involvement, in terms of being informed and welcomed, led to an improved ability to care for their loved ones. Emotionally supportive interventions targeting families should be considered in relation to a loved one's open-heart surgery.