Open-heart surgery patients face many problems because of post-sternotomy pain. Care protocols can eliminate pain and pain-related problems by providing holistic care. The aim of this study was to examine the effect of an open-heart surgery patient care protocol developed in the study on post-sternotomy pain, anxiety and quality of care. The study was carried out as a double-blind randomized controlled trial. The sample size was calculated. Considering some attrition, the sample size was increased by 10% for each group, and a total of 68 participants, including 34 in each group, were included in the sample. Data were collected using a 'Patient Information Form', a 'Post-Sternotomy Pain Follow-up Form', the 'Numeric Rating Scale', the 'State Anxiety Inventory' and the 'Strategic and Clinical Quality Indicators in Postoperative Pain Management Questionnaire'. The patients in the experimental group were given care in accordance with the protocol, which was developed in the study, on postoperative days 0, 1 and 2. The statistical evaluation showed a significant difference between the mean scores of the experimental (F = 7.28; p < .001) and control groups (F = 2.42; p < .05) on the pain assessment scale. It was determined that the number of analgesics used in the experimental group was statistically significantly lower than in the control group. Intra-group comparisons showed that there was a difference between the mean pre-test and post-test state anxiety scale scores of the groups (p < .001). The experimental group had higher mean scores on the Strategic and Clinical Quality Indicators in Postoperative Pain Management Questionnaire than that of the control group (p < .001). The protocol developed in the study was found to be effective in reducing pain, the use of NSAIDs and opioids, and anxiety levels and increasing the level of quality of care. The protocol was original and feasible in that it included independent nursing interventions to improve the quality of care by reducing pain and anxiety. Particularly, the use of protocols in intensive care units was nurses' strongest resource in patient care management. Thus, the protocol, which was prepared for intensive care patients who most frequently experience pain and anxiety, was promising for nurses in improving the quality of care by reducing pain and anxiety. However, it is necessary to conduct further studies involving longitudinal follow-up in samples and institutions with similar conditions.