OBJECTIVE: Doctors should involve their patients in making decisions about their care. We studied patients with heart disease to assess if shared decision-making occurs and to study factors that predict patients' choices or influence cardiologists' behaviour. METHODS: 85 patients attending for arteriography were assessed to elicit preferred involvement in decision-making, perception of involvement, and confidence in the decision. RESULTS: 40% of patients wished to be involved in decisions. Preferences were unrelated to demographic factors. Cardiologists involved patients more in decisions concerning severe disease (p=0.056). Involvement varied between cardiologists (p=0.001). The mean duration of consultations was 5.5 min. Patients' confidence in decisions correlated with duration (p=0.001), explicit reference to a decision that needed to be made (p=0.0026), and perceived, but not observed, involvement in decision-making (p=0.05). CONCLUSION: This study highlighted the complexity of doctor-patient communication. Irrespective of preferences for involvement, patients were more confident in decisions in which they perceived more involvement or which were the products of longer consultations. PRACTICE IMPLICATIONS: Patients' confidence in clinical decisions can be increased by increasing consultation length and increasing their perception of involvement. Patients perceive more involvement in decisions when doctors specifically identify the need for treatment decisions early in the consultation.