Abstract Aim To test the Theory of Adherence of People with Chronic Disease with regard to adherence to treatment among patients with coronary heart disease after a percutaneous coronary intervention. Background Increased knowledge of the concept of adherence is needed for the development of nursing interventions and nursing guidelines for patients with coronary heart disease. Design A cross‐sectional, multi‐centre study. Methods This study was conducted from February–December 2013 with 416 patients with coronary heart disease 4 months after undergoing a percutaneous coronary intervention. A self‐reported questionnaire was used to assess their adherence to treatment. Data were analysed using structural equation modelling. Results The theory explained 45% of the adherence to a healthy lifestyle and 7% of the adherence to medication. Structural equation modelling confirmed that motivation and results of care had the highest association with adherence to a healthy lifestyle. Responsibility was associated with adherence to medication. Support from next of kin, support from nurses and physicians, and motivation, co‐operation, fear of complications and a sense of normality were associated with adherence. Conclusion Patients who are motivated to perform self‐care and consider the results of care to be important were more likely to adhere to a healthy lifestyle. Responsible patients were more likely to adhere to their medication. It is important to account for these elements as a part of secondary prevention strategies among patients with coronary heart disease after a percutaneous coronary intervention.