AIMS AND OBJECTIVES: To explore the beliefs patients with heart failure hold about their illness and its treatment using the common-sense model of illness cognitions and behaviour as the theoretical framework. BACKGROUND: Heart failure is a disabling condition, which has a significant impact on individuals, their families and healthcare provision. The common-sense model provides a framework within which lay beliefs about illness and its treatment can be examined. Previous studies have reported a number of misconceptions in relation to the nature of and treatment for heart failure. Inaccurate beliefs are related to limited self-care and nonadherence to medication. DESIGN: A qualitative research design was used in which thematic analysis was used to interpret interview data. METHODS: Semi-structured interviews were carried out with twelve patients with chronic heart failure in a community setting in South East England. An interview schedule based on the dimensions of the common-sense model guided data collection. Data were analysed thematically using the framework method. RESULTS: A cluster of beliefs around a chronic illness with serious consequences was found. However, patients were unable to distinguish between symptoms of heart failure, effects of medication and emotional responses to the illness. The illness was attributed to external factors, especially stressful life events. There was a strong belief in the necessity of medication coupled with the belief that the illness and its symptoms could be controlled by medication. Concerns about drug interactions and side effects were prevalent. CONCLUSIONS: This study highlights the need for nurses to explore illness representations and treatment beliefs in heart failure. Misconceptions should be corrected to influence behaviour change. RELEVANCE TO CLINICAL PRACTICE: An understanding of illness representations and treatment beliefs should enable structured interventions to be developed, which improve clinical outcomes in this population.