INTRODUCTION: Cardiac rehabilitation is known to reduce morbidity and improve quality of life in people living with heart disease, however, adherence, access and completion of these programmes is suboptimal. Peer support may offer an opportunity to close this service gap. The aim of the study is to determine whether the effectiveness of a digital peer support programme for people living with heart disease is effective in improving social connectedness, clinical and patient-reported outcomes and experience measures. METHODS AND ANALYSIS: Heart2Heart is a community-based randomised controlled trial with 6 months follow-up for the primary outcome and 6 and 12 months for secondary outcomes. Approximately 752 adults with a diagnosis of heart disease in the past 12 months will be recruited from the general community and Australian cardiac rehabilitation programmes. Control group will participate in usual care, while intervention group will have access to a 6 months intervention that enables peer support via an interactive mobile application, in addition to usual care. The intervention includes online discussion groups, access to resources and facilitated conversations with health professionals. Primary outcome is social connectedness at 6 months follow-up. Secondary outcomes (6 and 12 months) will be all-cause/cardiovascular disease hospital admissions, all-cause mortality, lifestyle (sufficiently physically active, not smoking, sufficient fruit and vegetable consumption), proportion taking prescribed medications and health service utilisation (medical appointments, cardiac rehabilitation, participation in any other in-person peer support activities). Patient-reported outcome and experience measures including self-efficacy, quality of life, satisfaction and programme engagement will be analysed at 6 months. Process measures will include application analytics, barriers and facilitators to engagement with the intervention from participant's perspective. An intention-to-treat analysis will be used. ETHICS AND DISSEMINATION: Ethical clearance was obtained from Western Sydney Local Health District Ethics Committee. Heart2Heart has potential to improve social connectedness and provide a valuable addition to traditional cardiac rehabilitation. TRIAL REGISTRATION NUMBER: ACTRN12624000386538.