Background: Self-care management of a low-sodium diet is a critical component of comprehensive heart failure (HF) treatment. Aims: The primary purpose of this study was to examine the effectiveness of an educational intervention on reducing the dietary sodium intake of patients with HF. Secondary purposes were to examine the effects of the intervention on attitudes, subjective norm, and perceived behavioural control towards following a low-sodium diet. Methods: This was a randomized clinical trial of an educational intervention based on The Theory of Planned Behavior. Patients were randomized to either a usual care (n=25) or intervention group (n=27) with data collection at baseline, 6 weeks, and 6 months. The intervention group received low-sodium diet instructions and the usual care group received no dietary instructions. Nutrition Data Systems-Research software was used to identify the sodium content of foods on food diaries. Attitudes, subjective norm, and perceived behavioural control were measured using the Dietary Sodium Restriction Questionnaire. Results: Analysis of covariance (between-subjects effects) revealed that dietary sodium intake did not differ between usual care and intervention groups at 6 weeks; however, dietary sodium intake was lower in the intervention group (F=7.3, df=1,29, p=0.01) at 6 months. Attitudes subscale scores were higher in the intervention group at 6 weeks (F=7.6, df=1, 38, p<0.01). Conclusion: Carefully designed educational programmes have the potential to produce desired patient outcomes such as low-sodium diet adherence in patients with heart failure.