Background and objectives: Physical activity is important for all heart failure (HF) patients to improve quality of life and physical function. Since adherence to physical activity is low and could differ between seasons, it is essential to explore factors related to change that may depend on seasonal changes. The purpose of this study was to describe the seasonal differences in physical activity and assess factors that influence these differences in a country with markedly different winter-to-summer weather conditions (in temperature, hours of daylight and snow fall). Methods: The study had a cross-sectional survey design. Outpatients with HF completed a questionnaire on physical activity, motivation and self-efficacy to exercise and I-IF symptom severity in the summer and the winter in a northern hemisphere country. We used analysis of variance to evaluate seasonal differences in physical activity, motivation, self-efficacy and HF symptom severity. Results: Eighty-seven patients with HF (29% women, mean age 70 +/- 9 years) were included and 35% performed less physical activity (METs) in the winter, compared to the summer. Increased symptom severity during the winter was associated with lower activity levels. Conclusion: One-third of the patients performed less physical activity during the winter compared to the summer, and this was associated with symptom severity. Decreased physical activity was not related with motivation and self-efficacy. This study emphasises the need for personalised physical activity programmes that also assess symptom severity and change in symptom severity depending between seasons. (C) 2019 The Authors. Published by Elsevier Inc.