The collection and use of clinical samples for research complied with the ethical principles stated in the “Declaration of Helsinki” and the Human Tissue Act and were covered by ethical approvals from the UK National Research Ethic Service NRES (Research Ethic Committee –REC- references 13/OL/1687 and 10/HO107/63). We collected leftover samples from patients undergoing aortic valve replacement (AVR). The total PF volume was collected immediately after opening of the pericardium using a 20 mL syringe and transported to the laboratory in a sterile 50 mL container. Peripheral blood was collected from an arterial line in citrate-containing vacutainers (BD). Samples of right atrial appendage (RAA) were collected just before cannulation of the right atrium, and samples of ascending thoracic aorta were collected from excessive tissue on closure of the aortotomy. These were immediately placed in RNA Later stabilizing solution (Thermo Fisher Scientific) and stored at −80°C until processed. Blood and PF were processed immediately after collection, as follows. To obtain plasma, the citrate-containing vacutainers were centrifuged at 1,500 × g, 4°C for 15 min, and the supernatant was collected. The supernatant underwent further centrifugation at 13,500 × g, room temperature (RT), for 5 min to deplete the sample of miRNA-rich platelets. The platelet-free fluid was centrifuged at 13,500 × g, RT, for 5 min to remove any remaining of cells. The final platelet-poor plasma, PF and tissue samples were stored at −80°C until required.