Aims Heart failure (HF) substantially limits the ability of patients to engage in physical activities. A detailed understanding of how patients experience these limitations is required to develop valid and sensitive measures for use in clinical research. This qualitative study was designed to provide a thorough description of how HF patients experience physical activity limitations in their daily lives. Methods and results Semi-structured interviews were conducted with 40 HF patients. Interview transcripts were coded with the aim of identifying key aspects of physical activity. Patients were divided between HF with preserved ejection fraction (n = 21, 52.5%) and HF with reduced ejection fraction (n = 19, 47.5%); the majority of patients were New York Heart Association Class II (n = 22, 52.5%) or Class III (n = 16, 40.0%). Relevant physical activity themes, including mobility and broader daily function areas, were identified. The most frequently reported mobility limitations involved difficulty walking (up a steep incline, up steps, and long distances), limited walking speed, difficulty standing for long periods of time, and difficulty carrying and lifting objects. These limitations were principally related to three HF symptoms: dyspnoea, tiredness/fatigue, and peripheral oedema. Patients adapted to their symptoms and related mobility limitations in several ways, including taking rests during an activity, doing an activity more slowly, and avoiding/refraining from an activity altogether. The broader daily function areas most commonly impacted by the mobility limitations were housework, exercising or playing sports, and going shopping. Conclusions Heart failure patients report numerous physical activity limitations. These specific mobility and daily function areas can be measured using clinical outcome assessments (e.g. patient-reported outcomes and performance outcomes) in clinical trials and observational research. Accelerometry can be used to contribute to a holistic picture of patient functioning by passively collecting this type of data.