Background: Lifestyle behaviours are important risk factors for coronary heart disease (CHD) and, hence, motivation for lifestyle changes is suggested to be a key factor in the success of cardiac rehabilitation and secondary prevention programmes. The motivation for changing lifestyle among people with CHD may be influenced by those with whom they have long-term, intimate relationships. Aims: This study explores the role of the relationship between people with CHD and those closest to them in making lifestyle changes. This includes investigating if patients and partners experience autonomy, competence, and relatedness, and what role communal, i.e. relationship-centred coping serves in relation to patients’ health behaviour. Methods: The study is based on semi-structured, in-depth interviews with 10 couples; people who have experienced acute coronary syndrome, and their partners. Participants had diverse histories of disease and social backgrounds. A three-stage interview process was undertaken including focus group interviews, couple interviews and individual interviews. A thematic analysis, inspired by the self-determination theory and the interdependence theory, was conducted. Results: Communal coping is evident in various forms, and at different levels, among people with CHD and their partners. Satisfaction with new lifestyle, ownership of change, confidence in ability to change, and emotional distress are all factors that affect how couples deal with lifestyle changes in the aftermath of CHD. Conclusions: Rehabilitation efforts, aimed at lifestyle changes, need to address each individual, as well as the dyadic interaction within couples. Incorporating a dyadic perspective in the rehabilitation process may lead to a reduction in motivational barriers to lifestyle changes.