Depression and anxiety are common among people who have experienced an acute coronary event (e.g., heart attack). Multidisciplinary cardiac rehabilitation programs often focus on reducing risk factors associated with future cardiac events, however, mental health interventions are not routinely available. Given known difficulties with access to mental health treatment, the present study sought to explore the efficacy and acceptability of an Internet-delivered cognitive behavioural therapy program () among participants who experienced an acute coronary event. The five-lesson course was delivered over eight weeks and was provided with brief weekly contact, via telephone and secure email with a guide. Participants were randomized to the ( = 25) or waiting-list control group ( = 28). Symptoms were assessed at pre-treatment, post-treatment, and four-week follow-up. Completion rates (84%) and satisfaction ratings (95%) were high. Statistically significant between-group improvements were observed for the treatment group on primary measures of general anxiety (Cohen’s = 1.62; 67% reduction), depression (Cohen’s = 1.09; 61% reduction), and physical activity levels (Cohen’s = 0.27; 70% increase). Statistically significant improvements were also observed on secondary measures of distress (Cohen’s = 0.98; 51% reduction), cardiac anxiety (Cohen’s = 0.92; 34% reduction), and mental-health quality of life (Cohen’s = 0.23; 24% improvement). The changes were maintained at four-week follow-up. The current findings add to the existing literature and highlight the potential of Internet-delivered cognitive behavioural therapy programs among participants who have experienced an acute coronary event.© 2020 The Authors.