BACKGROUND Coronary heart disease (CHD) risk factor reduction is required to maximize the benefits to be gained from coronary artery bypass grafting. Risk factor reduction after surgery, however, is often incomplete and adherence rates are poor. The health behaviors of the cardiac partner can be supportive or can act to undermine the patient's motivation for change in risk factors. Concordance in health behaviors in couples can make it more difficult for patients to engage in positive lifestyle changes. OBJECTIVES The aims of this study were to increase understanding of the role of concordance in CHD risk factors and common medical conditions in patients and partners before and 4 months after bypass grafting and to examine changes in the pattern of concordance over time. METHODS A prospective study of patients' and partners' CHD risk factors was conducted in the outpatient clinic before and at home 4 months after bypass grafting. RESULTS There was significant concordance for preoperative physical activity, body mass index, and diabetes mellitus, and postoperatively, there was significant concordance for smoking status, physical activity, body mass index, cholesterol, and diabetes mellitus. There were significant associations between patients' preoperative and postoperative physical activity and cholesterol and between the partners' preoperative and postoperative physical activity. There was a significant change in the pattern of concordance for physical activity from preoperation to postoperation, with more patients but not partners increasing their physical activity levels. CONCLUSIONS Results revealed significant concordance in CHD risk factors and common medical conditions in patients and partners before and 4 months after coronary artery bypass grafting. This indicates that the behaviors of some couples can make it more difficult for patients to change their lifestyle. The health professionals involved in educating patients before and after bypass grafting need to target the patient and partner as a couple to help achieve more successful risk factor reduction.