Abstract Funding Acknowledgements Type of funding sources: Foundation. Main funding source(s): Dutch Heart Foundation - senior E-Dekker grant Physical activity and sedentary behaviour in cardiovascular disease patients during the COVID-19 lockdown in the Netherlands; a longitudinal cohort study Background Previous studies showed that the COVID-19 lockdown caused a more inactive lifestyle, but it is unknown whether these acute effects persist over time. We prospectively evaluated changes in physical activity and sedentary behaviour among chronic cardiovascular disease (CVD) patients during the first-wave COVID-19 lockdown and aimed to identify factors associated with physical inactivity. Methods 1,565 CVD patients were included and baseline physical activity and sedentary behaviour were assessed using validated questionnaires at 5 weeks after the initiation of the Dutch lockdown (March 2020). Follow-up measures were collected every subsequent 4 weeks until July 2020. Multivariate mixed model analyses were performed to identify whether age, gender, CVD subtype, lockdown adherence and mental health factors impacted changes in physical (in)activity. Results Patients were 67 (interquartile range [60, 73]) years, mostly male (73%) and primarily diagnosed with myocardial infarction (48%) or angina pectoris (18%). Daily time spent in moderate-to-vigorous physical activity was 143 minutes (95% confidence interval (CI) 137; 148) at baseline, with almost no changes during follow-up on a group level (Δ+8.0 (95%CI -1.1; 17.0); Δ+11.2 (95%CI 1.9; 20.5) and Δ+8.0 (95%CI -1.5; 17.5) min/day after 4, 8 and 12 weeks, respectively).Female gender (Δ-40.7 (95%CI -48.5; -33.0) min/day); heart failure (Δ-23.0 (95%CI -36.5; -9.5) min/day); fear of a COVID-19 infection (Δ-6.6 (95%CI -9.4; -3.8) min/day) and limited possibilities for physical activity (Δ-7.4 (95%CI -10.1; -4.7) min/day) were independently associated with a decrease in physical activity. Sedentary time was 567 (95%CI 555; 578) min/day at baseline which did not change ...