Background: The coronavirus (COVID-19) pandemic affects cardiovascular diseases MESHD (CVDs) directly through infection MESHD and indirectly through health service reorganisation and public health policy. Real-time data are needed to quantify direct and indirect effects. We aimed to monitor hospital activity for presentation, diagnosis and treatment of CVDs during the pandemic to inform on indirect effects. Methods: We analysed aggregate data on presentations, diagnoses and treatments or procedures for selected CVDs ( acute coronary syndromes MESHD, heart failure MESHD, stroke MESHD stroke HP and transient ischaemic attack, venous thromboembolism MESHD thromboembolism HP, peripheral arterial disease MESHD and aortic aneurysm MESHD aortic aneurysm HP) in UK hospitals before and during the COVID-19 epidemic. We produced an online visualisation tool to enable near real-time monitoring of trends. Findings: Nine hospitals across England and Scotland contributed hospital activity data from 28 Oct 2019 (pre-COVID-19) to 10 May 2020 (pre-easing of lockdown), and for the same weeks during 2018-2019. Across all hospitals, total admissions and emergency MESHD department (ED) attendances decreased after lockdown (23 March 2020) by 57.9% (57.1-58.6%) and 52.9% (52.2-53.5%) respectively compared with the previous year. Activity for cardiac, cerebrovascular and other vascular conditions started to decline 1-2 weeks before lockdown, and fell HP by 31-88% after lockdown, with the greatest reductions observed for coronary artery bypass grafts, carotid endarterectomy, aortic aneurysm MESHD aortic aneurysm HP repair and peripheral arterial disease MESHD procedures. Compared with before the first UK COVID-19 (31 January 2020), activity declined across diseases MESHD and specialties between the first case and lockdown (total ED attendances RR 0.94, 0.93-0.95; total hospital admissions RR 0.96, 0.95-0.97) and after lockdown (attendances RR 0.63, 0.62-0.64; admissions RR 0.59, 0.57-0.60). There was limited recovery towards usual levels of some activities from mid-April 2020. Interpretation: Substantial reductions in total and cardiovascular activities are likely to contribute to a major burden of indirect effects of the pandemic, suggesting they should be monitored and mitigated urgently.