Introduction Many hospital presentations for acute coronary syndrome (ACS) occur in people previously hospitalised with coronary heart disease (CHD), leading to increased costs and health burden. Secondary prevention education including a prehospital discharge plan is recommended for all individuals to reduce the risk of recurrence. However, many clinicians lack the time or support to provide education, and patients’ uptake of secondary prevention programmes is limited. An avatar-based education app is a novel and engaging way to provide self-delivered, evidence-based secondary prevention information during the hospital admission and remains accessible after discharge. This protocol aims to evaluate the effect of an avatar-based education app on individuals with ACS. Methods and analysis This protocol describes a prospective, randomised controlled trial with 3-month follow-up and blinded assessment of 72 participants. Intervention group participants will download the app onto their own device during the hospital admission and independently complete six interactive education modules based on the National Heart Foundation’s six steps to cardiac recovery. All participants will receive a text message reminder of the study after 3 weeks. Both groups will receive usual care consisting of bedside education and a pamphlet about cardiac rehabilitation. The primary outcome is knowledge of CHD, assessed using the Coronary Artery Disease Education Questionnaire II. Secondary outcomes include quality of life, response to heart attack symptoms, cardiac-related readmissions and mortality and modifiable cardiac risk factors. Engagement with the app will be evaluated objectively. Intention-to-treat analysis will be conducted, with between-group comparisons and 95% CIs of the primary outcome analysed using analysis of covariance, adjusting for baseline values. Ethics and dissemination This study protocol has been approved by the Western Sydney Local Health District Human Research Ethics Committee. The results of this study will be disseminated via a peer-reviewed journal and research thesis. Trial registration number Australian New Zealand Clinical Trials Registry (ACTRN12622001436763).