Previous studies offer contradictory evidence regarding the effects of cortisol changes on health outcomes for surgical heart patients. Increased cortisol and inflammation have been related to psychological stress while separate studies have found an inverse relation between cortisol and inflammation. Psychological preparations for surgery can reduce stress and improve outcomes and may interact with cortisol changes. Following from these relationships, we hypothesised that a preparation for surgery will interact with changes in cortisol to affect outcomes. Measures were the SF 36 General Health and Activities, medical visits and satisfaction. Eighty-five patients were randomly assigned to standard care plus a psychological preparation or standard care alone using a single-blind methodology. Data on psychological and biological functioning were collected at admission, 1 day prior and 5 days post-surgery, and 12-months after hospital discharge. General health and activities, and medical visits were related to the interaction of cortisol change and psychological preparation in support of the hypothesis. Patients were more satisfied in the preparation group than controls. Based on these findings, some outcomes from psychological preparations may be affected by changes in levels of cortisol. These results caution against a one-size-fits-all approach to psychological preparations.