OBJECTIVE:To investigate clinically relevant intra-individual and mean changes in health-related quality of life (HRQoL) with the Short Form-36 Health Survey (SF-36) need to acknowledge that SF-36 is trademarked ie: SF-36(R) following cardiac intervention for Australian and Danish patients. DESIGN:Prospective observational study in tertiary cardiac centres in Townsville, Queensland, Australia and Copenhagen, Denmark. Two hundred coronary artery bypass graft surgery (CABG) patients of two Townsville hospitals, and 47 CABG or percutaneous coronary intervention (PCI) patients of a Copenhagen hospital. The main outcome measures are eight SF-36 health subscales at baseline and six months post-intervention. RESULTS:Australian and Danish patients experienced similar HRQoL pre-intervention. By six months post-intervention, patients experienced a significant mean improvement in all subscales of the SF-36 survey (p < or = 0.05), although up to 27% of patients had a clinically significant decline in HRQoL from baseline. CONCLUSIONS:These results demonstrate that it is necessary to investigate intra-individual changes in HRQoL as well as group mean changes as they produce different conclusions. In addition, establishing clinically significant intra-individual change standards may assist researchers and clinicians in determining whether an individual may benefit from therapy or intervention.