Objectives.Cardiac patients have been shown to have inaccurate understanding of their cardiovascular risk. The purpose of the study was to investigate whether a guideline‐based risk assessment and management intervention could facilitate understanding of cadiovascular risk and appropriate illness perceptions in cardiac patients.Design.Randomized trial.Methods.A total of 106 patients with MI or unstable angina were randomized to receive standard care with or without a 30‐min nurse‐led computerized Predict CVD‐Diabetes (where CVD is cardiovascular disease) session. Patients’ risk perceptions (using categorical and numerical measures), and perceptions of their heart condition were assessed at admission, discharge, and 3 months.Results.The intervention group rated the risk information as more easily understood than the control group. At discharge, they had increased perceptions of personal control, higher perceptions that a low‐fat diet and regular exercise could help their condition, and believed their current illness would be shorter compared to the control group. At 3 months, no group differences were significant. The intervention had no effect on risk perceptions, which were high in both groups. Patients’ perceptions of ‘high’ risk corresponded to numerical estimates of over 50%, which differs from clinical guidelines (over 20%).Conclusions.A computerized cardiovascular risk assessment and management session can help acute coronary syndrome patients understand CVD risk information and improve perceptions of control in the short term, but not change risk perceptions. In‐hospital risk factor assessment and management information may help patients understand the importance of key lifestyle changes.Statement of contributionWhat is already known on this subject?• Many members of the public, as well as patients with diagnosed coronary heart disease (CHD), have poor understanding of their cardiovascular disease risk.• Giving risk information can improve accuracy of risk perceptions, and may increase intentions to start preventive risk reduction treatments but more research is needed with patients with established CHD.What does this study add?• Providing acute coronary syndrome patients with individualised risk assessment and risk management information may be beneficial over the short term by increasing patients' perceptions of control and the importance of key lifestyle changes.• A difficulty in communicating cardiovascular risk levels is the poor correspondence between patients' understanding of very high risk and the cl